include/asm-*/system.h: remove unused set_rmb(), set_wmb() macros

These don't appear anywhere else in the kernel anymore.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>