Miscellaneous doc fixes for v1.2 ...

Change-Id: I6f49bd779f2a4d577c6443dd160290656cdbc59b

Documentation updates for the new GIC drivers ...

This patch updates the relevant documentation in ARM Trusted Firmware
for the new GIC drivers. The user-guide.md and porting-guide.md have been
updated as follows:

*  The build option to compile Trusted Firmware with different GIC drivers
   for FVP has been explained in the user-guide.md.

*  The implementation details of interrupt management framework porting
   APIs for GICv3 have been added in porting-guide.md.

*  The Linaro tracking kernel release does not work OOB in GICv3 mode.
   The instructions for changing UEFI configuration in order to run with
   the new GICv3 driver in ARM TF have been added to user-guide.md.

The interrupt-framework-design.md has been updated as follows:

*  Describes support for registering and handling interrupts targeted to EL3
   e.g. Group 0 interrupts in GICv3.

*  Describes the build option `TSP_NS_INTR_ASYNC_PREEMPT` in detail.

*  Describes preemption of TSP in S-EL1 by non secure interrupts and
   also possibly by higher priority EL3 interrupts.

*  Describes the normal world sequence for issuing `standard` SMC calls.

*  Modifies the document to correspond to the current state of interrupt
   handling in TSPD and TSP.

*  Modifies the various functions names in the document to reflect
   the current names used in code.

Change-Id: I78c9514b5be834f193405aad3c1752a4a9e27a6c

Enable use of FIQs and IRQs as TSP interrupts ...

On a GICv2 system, interrupts that should be handled in the secure world are
typically signalled as FIQs. On a GICv3 system, these interrupts are signalled
as IRQs instead. The mechanism for handling both types of interrupts is the same
in both cases. This patch enables the TSP to run on a GICv3 system by:

1. adding support for handling IRQs in the exception handling code.
2. removing use of "fiq" in the names of data structures, macros and functions.

The build option TSPD_ROUTE_IRQ_TO_EL3 is deprecated and is replaced with a
new build flag TSP_NS_INTR_ASYNC_PREEMPT. For compatibility reasons, if the
former build flag is defined, it will be used to define the value for the
new build flag. The documentation is also updated accordingly.

Change-Id: I1807d371f41c3656322dd259340a57649833065e

Remove the IMF_READ_INTERRUPT_ID build option ...

The IMF_READ_INTERRUPT_ID build option enables a feature where the interrupt
ID of the highest priority pending interrupt is passed as a parameter to the
interrupt handler registered for that type of interrupt. This additional read
of highest pending interrupt id from GIC is problematic as it is possible that
the original interrupt may get deasserted and another interrupt of different
type maybe become the highest pending interrupt. Hence it is safer to prevent
such behaviour by removing the IMF_READ_INTERRUPT_ID build option.

The `id` parameter of the interrupt handler `interrupt_type_handler_t` is
now made a reserved parameter with this patch. It will always contain
INTR_ID_UNAVAILABLE.

Fixes ARM-software/tf-issues#307

Change-Id: I2173aae1dd37edad7ba6bdfb1a99868635fa34de

Some minor fixes to interrupt-framework-design.md ...

This patch fixes a pair of typos. The security state had been described
as non-secure where it should have been secure.

Change-Id: Ib3f424708a6b8e2084e5447f8507ea4e9c99ee79

Create Table of Content links in markdown files ...

Fixes arm-software/tf-issues#276

Miscellaneous documentation fixes ...

This patch gathers miscellaneous minor fixes to the documentation, and comments
in the source code.

Change-Id: I631e3dda5abafa2d90f464edaee069a1e58b751b
Co-Authored-By: Soby Mathew <soby.mathew@arm.com>
Co-Authored-By: Dan Handley <dan.handley@arm.com>

Document design of the Interrupt Mangement Framework ...

This patch adds documentation that describes the design of the Interrupt
management framework in the ARM Trusted Firmware. The porting-guide.md has also
been updated to describe the interface that should be implemented by each
platform to support this framework.

Change-Id: I3eda48e5c9456e6a9516956bee16a29e366633b7
Co-Authored-By: Soby Mathew <soby.mathew@arm.com>