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

Remove re-initialisation of system timers after warm boot for FVP ...

This patch removes the reinitialisation of memory mapped system timer
registers after a warm boot for the FVP. The system timers in FVP are
in the 'Always ON' power domain which meant the reinitialisation was
redundant and it could have conflicted with the setup the normal
world has done.

The programming of CNTACR(x) and CNTNSAR, the system timer registers,
are removed from the warm boot path with this patch.

Fixes ARM-software/tf-issues#169

Change-Id: Ie982eb03d1836b15ef3cf1568de2ea68a08b443e

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