aarch64: Add vector implementations of exp routines

Optimised implementations for single and double precision, Advanced
SIMD and SVE, copied from Arm Optimized Routines.

As previously, data tables are used via a barrier to prevent
overly aggressive constant inlining. Special-case handlers are
marked NOINLINE to avoid incurring the penalty of switching call
standards unnecessarily.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>