aarch64,falkor: Use vector registers for memcpy

Vector registers perform better than scalar register pairs for copying
data so prefer them instead.  This results in a time reduction of over
50% (i.e. 2x speed improvemnet) for some smaller sizes for memcpy-walk.
Larger sizes show improvements of around 1% to 2%.  memcpy-random shows
a very small improvement, in the range of 1-2%.

	* sysdeps/aarch64/multiarch/memcpy_falkor.S (__memcpy_falkor):
	Use vector registers.

(cherry picked from commit 0aec4c1d)