s390/ap: Restrict driver_override versus apmask and aqmask use

s390/ap: Restrict driver_override versus apmask and aqmask use

Introduce a restriction for the driver_override feature versus apmask
and aqmask:
- driver_override is only allowed when the apmask and aqmask values
  both are default (=0xffff..ffff).
- apmask and aqmask modifications are only allowed when there is no
  driver_override on any AP device active.
So in the end the user is restricted to choose to either use
apmask/apmask to divide the AP devices into host owned and vfio owned
or use the driver_override feature but not mix these two approaches.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>