s390/bear: Convert cpu_has_bear() to cpu feature function

Get rid of the cpu_has_bear jump label and convert cpu_has_bear() to a cpu
feature function using test_facility() and with that use a static branch.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>