[S390] cleanup bitops.h.

Encapsulate complete bitops.h with #ifdef __KERNEL__ and remove the now
superfluous ALIGN_CS define and its users.
This patch is needed for compiling klibc.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>