s390: cleanup and add sanity checks to control register macros

- turn some macros into functions
- merge two almost identical versions for 32/64 bit
- add BUILD_BUG_ON() check to make sure the passed in array is large enough

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