NEON: added an ARM assembly source file with some helper functions

These should be useful for implementing NEON optimized overlapped blit.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
NEON: Added overlapped blit implementation and runtime CPU detection

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