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

Refactor fvp_config into common platform header ...

Changed the fvp_config array in fvp_common.c into a struct and
moved into a new optional common platform header,
include/plat/common/plat_config.h. Removed the config definitions
in fvp_def.h and updated all references to the platform config.

This makes the interface to the platform config cleaner and uses
a little less RAM.

Fixes ARM-software/tf-issues#180

Change-Id: I58dd7b3c150f24f7ee230a26fd57c827853ba803

Simplify entry point information generation code on FVP ...

This patch reworks FVP specific code responsible for determining
the entry point information for BL3-2 and BL3-3 stages when BL3-1
is configured as the reset handler.

Change-Id: Ia661ff0a6a44c7aabb0b6c1684b2e8d3642d11ec

Rename FVP specific files and functions ...

FVP specific files and functions containing the word "plat" have been
renamed to use the word "fvp" to distinguish them from the common
platform functionality and porting functions.

Change-Id: I39f9673dab3ee9c74bd18b3e62b7c21027232f7d

Move BL porting functions into platform.h ...

Some platform porting functions were in BL specific header files.
These have been moved to platform.h so that all porting functions
are in the same place. The functions are now grouped by BL.
Obsolete BL headers files have been removed.

Also, the weak declaration of the init_bl2_mem_layout() function
has been moved out the header file and into the source file
(bl_common.c) using the more succinct #pragma syntax. This
mitigates the risk of 2 weak definitions being created and the
wrong one being picked up by the compiler.

Change-Id: Ib19934939fd755f3e5a5a5bceec88da684308a83

Split platform.h into separate headers ...

Previously, platform.h contained many declarations and definitions
used for different purposes. This file has been split so that:

* Platform definitions used by common code that must be defined
  by the platform are now in platform_def.h. The exact include
  path is exported through $PLAT_INCLUDES in the platform makefile.

* Platform definitions specific to the FVP platform are now in
  /plat/fvp/fvp_def.h.

* Platform API declarations specific to the FVP platform are now
  in /plat/fvp/fvp_private.h.

* The remaining platform API declarations that must be ported by
  each platform are still in platform.h but this file has been
  moved to /include/plat/common since this can be shared by all
  platforms.

Change-Id: Ieb3bb22fbab3ee8027413c6b39a783534aee474a