When calling e.g. atomic_sub_return with a large constant, the
compiler may output an immediate that is too large for the sub
instruction in the middle of the loop.

Fix this by explicitly specifying the number of bits allowed in the
constraint. Also stop atomic_add_return() and friends from falling
back to their respective "sub" variants if the constant is too large
to fit in an immediate.
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>