ArmPkg/CompilerIntrinsicesLib: Fixed memmove() and memset()

ArmPkg/CompilerIntrinsicesLib: Fixed memmove() and memset()

- Fixed memmove when going backward: the copy started one byte
  after the end of the region to copy
- memset: - removed unused register
          - fixed arguments size and character arguments were
            actually reversed
- Added memmove() to ARM32 GCC

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16328 6f19259b-4bc3-4df7-8a09-765794883524