MdePkg/BaseMemoryLibOptDxe: replace deprecated uses of IT blocks

MdePkg/BaseMemoryLibOptDxe: replace deprecated uses of IT blocks

The ARM architecture version 8 deprecates all uses of the IT instruction
except cases where it is followed by a single narrow instruction. So
replace any occurrences with equivalent sequences that adhere to the
new rules.

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