s390x/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.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Merge remote-tracking branch 'remotes/cohuck/tags/virtio-ccw-20140305' into staging

One patch introducing support for adapter interrupts in virtio-ccw.

This improves performance for those guests that issue the new
CCW_CMD_SET_IND_ADAPTER channel command.

# gpg: Signature made Wed 05 Mar 2014 08:48:18 GMT using RSA key ID C6F02FAF
# gpg: Can't check signature: public key not found

* remotes/cohuck/tags/virtio-ccw-20140305:
  s390x/virtio-ccw: Adapter interrupt support.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>