s390/ipl: add common ipl parameter attribute group

All ipl types have 'secure','has_secure' and type parameters. Move
these to a common ipl parameter group so that they don't need to be
present in each ipl parameter group.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>