chore(simd): remove unused macros and utilities for FP

Now that we have switched to simd context save/restore apis
which uses simd_context_t data structures, we can safely remove
any macros, helpers and utilities used in the old way of
FPU context management.

Change-Id: I27a636dd07bf5c4cb99fd25b9a204d55b525b677
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>