qxl: add QXL_IO_FLUSH_{SURFACES,RELEASE} for guest S3&S4 support

qxl: add QXL_IO_FLUSH_{SURFACES,RELEASE} for guest S3&S4 support

Add two new IOs.
 QXL_IO_FLUSH_SURFACES - equivalent to update area for all surfaces, used
  to reduce vmexits from NumSurfaces to 1 on guest S3, S4 and resolution change (windows
  driver implementation is such that this is done on each of those occasions).
 QXL_IO_FLUSH_RELEASE - used to ensure anything on last_release is put on the release ring
  for the client to free.

Signed-off-by: Yonit Halperin <yhalperi@redhat.com>
Signed-off-by: Alon Levy <alevy@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>