s390/boot: move detect_facilities() after cmd line parsing

Facilities setup has to be done after "facilities" command line option
parsing, it might set extra or remove existing facilities bits for
testing purposes.

Fixes: bb1520d5 ("s390/mm: start kernel with DAT enabled")
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>