power: improve inline asm memory constraints

Use "+m" rather than a combination of "=m" and "m" for improved
clarity and consistency.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --cc include/asm-powerpc/atomic.h
Simple merge

diff --cc include/asm-powerpc/bitops.h
Simple merge

diff --cc include/asm-powerpc/system.h
Simple merge