MdePkg/BaseMemoryLibOptDxe: add accelerated AARCH64 routines

This adds AARCH64 support to BaseMemoryLibOptDxe, based on the cortex-strings
library. All string routines are accelerated except ScanMem16, ScanMem32,
ScanMem64 and IsZeroBuffer, which can wait for another day. (Very few
occurrences exist in the codebase)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>