feat(simd): add sve state to simd ctxt struct

This patch extends the simd data structure to hold the SVE state. A new
build flag CTX_INCLUDE_SVE_REGS is introduced in this patch to enable
SVE context management.

Necessary precautions are taken such as ensuring the field offsets are
not changed and necessary padding is added for alignment reasons.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Signed-off-by: Okash Khawaja <okash@google.com>
Change-Id: I54f5222c7d8c68638105003f68caa511d347cd60