sparc64: Add SPARC-T4 optimized memcpy.

		Before		After
		--------------	--------------
bw_tcp:         1288.53 MB/sec	1637.77 MB/sec
bw_pipe:        1517.18 MB/sec	2107.61 MB/sec
bw_unix:        1838.38 MB/sec	2640.91 MB/sec

make -s -j128
allmodconfig	5min 49sec	5min 31sec

Signed-off-by: David S. Miller <davem@davemloft.net>