MdePkg/BaseMemoryLib: widen aligned accesses to 32 or 64 bits

MdePkg/BaseMemoryLib: widen aligned accesses to 32 or 64 bits

Since the default BaseMemoryLib should be callable from any context,
including ones where unaligned accesses are not allowed, it implements
InternalCopyMem() and InternalSetMem() using byte accesses only.
However, especially in a context where the MMU is off, such narrow
accesses may be disproportionately costly, and so if the size and
alignment of the access allow it, use 32-bit or even 64-bit loads and
stores (the latter may be beneficial even on a 32-bit architectures like
ARM, which has load pair/store pair instructions)

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