Improvements to ARM GIC driver ...

This patch introduces several improvements to the ARM GIC driver:

* In function gicd_set_itargetsr(), target CPU is specified using
  the same bit mask detailed in the GICD_ITARGETSRn register instead
  of the CPU linear ID, removing the dependency between bit position
  and linear ID in the platform porting. The current CPU bit mask
  may be obtained by reading GICD_ITARGETSR0.

* PPIs and SGIs are initialized in arm_gic_pcpu_distif_setup().
  SPIs are initialized in arm_gic_distif_setup().

* By default, non secure interrupts are assigned the maximum
  priority allowed to a non secure interrupt (defined by
  GIC_HIGHEST_NS_PRIORITY).

* GICR base address is allowed to be NULL for GICv1 and GICv2.

Change-Id: Ie2837fe860d43b2282e582dfdb13c39c6186f232

Rework incorrect use of assert() and panic() in codebase ...

Assert a valid security state using the macro sec_state_is_valid().
Replace assert() with panic() in those cases that might arise
because of runtime errors and not programming errors.
Replace panic() with assert() in those cases that might arise
because of programming errors.

Fixes ARM-software/tf-issues#96

Change-Id: I51e9ef0439fd5ff5e0edfef49050b69804bf14d5

Refactor fvp gic code to be a generic driver ...

Refactor the FVP gic code in plat/fvp/fvp_gic.c to be a generic ARM
GIC driver in drivers/arm/gic/arm_gic.c. Provide the platform
specific inputs in the arm_gic_setup() function so that the driver
has no explicit dependency on platform code.

Provide weak implementations of the platform interrupt controller
API in a new file, plat/common/plat_gic.c. These simply call through
to the ARM GIC driver.

Move the only remaining FVP GIC function, fvp_gic_init() to
plat/fvp/aarch64/fvp_common.c and remove plat/fvp/fvp_gic.c

Fixes ARM-software/tf-issues#182

Change-Id: Iea82fe095fad62dd33ba9efbddd48c57717edd21

Make system register functions inline assembly ...

Replace the current out-of-line assembler implementations of
the system register and system instruction operations with
inline assembler.

This enables better compiler optimisation and code generation
when accessing system registers.

Fixes ARM-software/tf-issues#91

Change-Id: I149af3a94e1e5e5140a3e44b9abfc37ba2324476

Introduce interrupt registration framework in BL3-1 ...

This patch introduces a framework for registering interrupts routed to
EL3. The interrupt routing model is governed by the SCR_EL3.IRQ and
FIQ bits and the security state an interrupt is generated in. The
framework recognizes three type of interrupts depending upon which
exception level and security state they should be handled in
i.e. Secure EL1 interrupts, Non-secure interrupts and EL3
interrupts. It provides an API and macros that allow a runtime service
to register an handler for a type of interrupt and specify the routing
model. The framework validates the routing model and uses the context
management framework to ensure that it is applied to the SCR_EL3 prior
to entry into the target security state. It saves the handler in
internal data structures. An API is provided to retrieve the handler
when an interrupt of a particular type is asserted. Registration is
expected to be done once by the primary CPU. The same handler and
routing model is used for all CPUs.

Support for EL3 interrupts will be added to the framework in the
future. A makefile flag has been added to allow the FVP port choose
between ARM GIC v2 and v3 support in EL3. The latter version is
currently unsupported.

A framework for handling interrupts in BL3-1 will be introduced in
subsequent patches. The default routing model in the absence of any
handlers expects no interrupts to be routed to EL3.

Change-Id: Idf7c023b34fcd4800a5980f2bef85e4b5c29e649

Fix C accessors to GIC distributor registers with set/clear semantics ...

This patch fixes C accessors to GIC registers that follow a set/clear
semantic to change the state of an interrupt, instead of read/write/modify.
These registers are:
  Set-Enable
  Clear-Enable
  Set-Pending
  Clear-Pending
  Set-Active
  Clear-Active
For instance, to enable an interrupt we write a one to the corresponding bit
in the Set-Enable register, whereas to disable it we write a one to the
corresponding bit in the Clear-Enable register.

Fixes ARM-software/tf-issues#137

Change-Id: I3b66bad94d0b28e0fe08c9042bac0bf5ffa07944

Correct usage of data and instruction barriers ...

The current code does not always use data and instruction
barriers as required by the architecture and frequently uses
barriers excessively due to their inclusion in all of the
write_*() helper functions.

Barriers should be used explicitly in assembler or C code
when modifying processor state that requires the barriers in
order to enable review of correctness of the code.

This patch removes the barriers from the helper functions and
introduces them as necessary elsewhere in the code.

PORTING NOTE: check any port of Trusted Firmware for use of
system register helper functions for reliance on the previous
barrier behaviour and add explicit barriers as necessary.

Fixes ARM-software/tf-issues#92

Change-Id: Ie63e187404ff10e0bdcb39292dd9066cb84c53bf

Reduce deep nesting of header files ...

Reduce the number of header files included from other header
files as much as possible without splitting the files. Use forward
declarations where possible. This allows removal of some unnecessary
"#ifndef __ASSEMBLY__" statements.

Also, review the .c and .S files for which header files really need
including and reorder the #include statements alphabetically.

Fixes ARM-software/tf-issues#31

Change-Id: Iec92fb976334c77453e010b60bcf56f3be72bd3e

Refactor GIC header files ...

Move the function prototypes from gic.h into either gic_v2.h or
gic_v3.h as appropriate. Update the source files to include the
correct headers.

Change-Id: I368cfda175cdcbd3a68f46e2332738ec49048e19

Move include and source files to logical locations ...

Move almost all system include files to a logical sub-directory
under ./include. The only remaining system include directories
not under ./include are specific to the platform. Move the
corresponding source files to match the include directory
structure.

Also remove pm.h as it is no longer used.

Change-Id: Ie5ea6368ec5fad459f3e8a802ad129135527f0b3