Add Siarhei Siamashka's optimized ARM memcpy, and update benchmark program

This commit adds Siarhei Siamashka's optimized ARM armv5memcpy from the
xf86-video-sunxi repository (https://github.com/ssvb/xf86-video-sunxi).
The benchmark program is extended with command line options and shows
the difference between three different memcpy implementations: default
libc, fastarm and ssvb's memcpy.

Results on the Allwinner platform show the libc memcpy does well, with
ssvb's memcpy being about as fast (with some small differences for
different tests). As expected, the experimental mostly C fastarm memcpy
is considerably slower for most cases. Besides thrashing the instruction
cache with a relatively large footprint, it also shows that on the ARM
platform hand-optimized assembler can beat the C compiler by a large
margin.