CPU: add ARM memcpy assembly function

This is my old ARM9E/ARM11 memcpy code from
    https://garage.maemo.org/projects/mplayer/
with some tuning for Raspberry Pi (aligned prefetch added).

Will be used by VFP optimized overlapped blt function.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>