KVM: s390: make kvm_s390_get_io_int() aware of GISA

The function returns a pending I/O interrupt with the highest
priority defined by its ISC.

Together with AIV activation, pending adapter interrupts are
managed by the GISA IPM. Thus kvm_s390_get_io_int() needs to
inspect the IPM as well when the interrupt with the highest
priority has to be identified.

In case classic and adapter interrupts with the same ISC are
pending, the classic interrupt will be returned first.

Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>