Replaced placeholder implementation of plat_set_nv_ctr for FVP
platforms by a working one.

On FVP, the mapping of region DEVICE2 has been changed from RO to RW
to prevent exceptions when writing to the NV counter, which is
contained in this region.

Change-Id: I56a49631432ce13905572378cbdf106f69c82f57

This patch adds support to select CCN driver for FVP during build.
A new build option `FVP_INTERCONNECT_DRIVER` is added to allow
selection between the CCI and CCN driver. Currently only the CCN-502
variant is supported on FVP.

The common ARM CCN platform helper file now verifies the cluster
count declared by platform is equal to the number of root node
masters exported by the ARM Standard platform.

Change-Id: I71d7b4785f8925ed499c153b2e9b9925fcefd57a

This patch removes support for legacy Versatile Express memory map for the
GIC peripheral in the FVP platform. The user guide is also updated for the
same.

Change-Id: Ib8cfb819083aca359e5b46b5757cb56cb0ea6533

This patch modifies the upstream platform port makefiles to use the new
xlat_tables library files. This patch also makes mmap region setup common
between AArch64 and AArch32 for FVP platform port. The file `fvp_common.c`
is moved from the `plat/arm/board/fvp/aarch64` folder to the parent folder
as it is not specific to AArch64.

Change-Id: Id2e9aac45e46227b6f83cccfd1e915404018ea0b