feat(fvp): allow SIMD context to be put in TZC DRAM

This patch demonstrates the capability of SEPARATE_SIMD_SECTION build
flag through which the memory intensive SIMD context data structures
are allocated in a separate section withtin the TZC DRAM space.

Change-Id: Idf3f232a7960a8f84f279d496c76953a6dad2009
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>