s390/bitops: Switch to generic bitops

The generic bitops implementation is nearly identical to the s390
implementation therefore switch to the generic variant.

This results in a small kernel image size decrease. This is because for
the generic variant the nr parameter for most bitops functions is of
type unsigned int while the s390 variant uses unsigned long.

bloat-o-meter:
add/remove: 670/670 grow/shrink: 167/209 up/down: 21440/-21792 (-352)

Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>