When vop is disabled and we read the vop register the system will
hang, so check vop status when we wait for the DMA finish flag to
avoid this sitiuation. This is done by checking for standby, DMA stop
mode, and disabled window states. Any one of these will prevent the
DMA finish flag from triggering.

Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Derek Basehore <dbasehore@chromium.org>