s390/virtio-ccw: Adapter interrupt support.

Handle the new CCW_CMD_SET_IND_ADAPTER command enabling adapter interrupts
on guest request. When active, host->guest notifications will be handled
via global_indicator -> queue indicators instead of queue indicators +
subchannel I/O interrupt. Indicators for virtqueues may be present at an
offset.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>