feat(simd): introduce simd context helper APIs

This patch adds the common API to save and restore FP and SVE. When SVE
is enabled we save and restore SVE which automatically covers FP. If FP
is enabled while SVE is not, then we save and restore FP only.

The patch uses simd_ctx_t to save and restore both FP and SVE which
means developers need not use fp or sve routines directly. Once all the
calls to fpregs_context_* are replaced with simd_ctx_*, we can remove
fp_regs_t data structure and macros (taken care in a following patch).

simd_ctx_t is currently allocated in section of its own. This will go
into  BSS section by default but platform will have option of relocating
it to a different section by overriding in plat.ld.S.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Signed-off-by: Okash Khawaja <okash@google.com>
Change-Id: I090f8b8fa3862e527b6c40385249adc69256bf24
diff --git a/Makefile b/Makefile
index d5a70ef..c99b4bb 100644
--- a/Makefile
+++ b/Makefile
@@ -1169,6 +1169,7 @@
 	SEPARATE_CODE_AND_RODATA \
 	SEPARATE_BL2_NOLOAD_REGION \
 	SEPARATE_NOBITS_REGION \
+	SEPARATE_SIMD_SECTION \
 	SPIN_ON_BL1_EXIT \
 	SPM_MM \
 	SPMC_AT_EL3 \
@@ -1342,6 +1343,7 @@
 	SEPARATE_CODE_AND_RODATA \
 	SEPARATE_BL2_NOLOAD_REGION \
 	SEPARATE_NOBITS_REGION \
+	SEPARATE_SIMD_SECTION \
 	RECLAIM_INIT_CODE \
 	SPD_${SPD} \
 	SPIN_ON_BL1_EXIT \