[SPARC64]: Don't use in/local regs for ldx/stx data in N1 memcpy.

It doesn't matter for use in 64-bit objects, but when used in
32-bit environments the top 32-bits of the local and in
registers will get chopped off on the next register window
spill/restore which leads to difficult to track down and
subtle bugs.

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