This patch adds AArch32 support for FVP and implements common platform APIs
like `plat_get_my_stack`, `plat_set_my_stack`, `plat_my_core_cos` for AArch32.
Only Multi Processor(MP) implementations of these functions are considered in
this patch. The ARM Standard platform layer helpers are implemented for
AArch32 and the common makefiles are modified to cater for both AArch64 and
AArch32 builds. Compatibility with the deprecated platform API is not
supported for AArch32.

Change-Id: Iad228400613eec91abf731b49e21a15bcf2833ea