AArch32: Add essential ARM platform and FVP support ...

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

Include `plat_psci_common.c` from the new location ...

The `plat_psci_common.c` was moved to the new location `plat/common`
and a stub file was retained at previous location for compatibility. This
patch modifies the platform makefiles to include the file from the new
location.

Change-Id: Iabddeeb824e9a5d72d176d7c644735966c8c0699

PSCI: Implement platform compatibility layer ...

The new PSCI topology framework and PSCI extended State framework introduces
a breaking change in the platform port APIs. To ease the migration of the
platform ports to the new porting interface, a compatibility layer is
introduced which essentially defines the new platform API in terms of the
old API. The old PSCI helpers to retrieve the power-state, its associated
fields and the highest coordinated physical OFF affinity level of a core
are also implemented for compatibility. This allows the existing
platform ports to work with the new PSCI framework without significant
rework. This layer will be enabled by default once the switch to the new
PSCI framework is done and is controlled by the build flag ENABLE_PLAT_COMPAT.

Change-Id: I4b17cac3a4f3375910a36dba6b03d8f1700d07e3