s390/facilities: optimize test_facility()

test_facility() can be optimized for bits which must be set anyway,
due to the check in head.S. This removes a couple of superfluous
runtime checks.

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