arm: optimize memcpy_{from,to}io() and memset_io

Optimize memcpy_{from,to}io() and memset_io() by transferring in
double words as much as possible with minimized barrier usage.
This simplest optimization brings faster throughput compare to
current byte-by-byte read and write with barrier in the loop.
This patch is based on arm64 optimization.

Change-Id: Ib0b67ba516c25a17047314ff916a348db07350e9
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>