drm/rockchip: vop: optimize register take effect check

drm/rockchip: vop: optimize register take effect check

Previous version check all the win, check its yrgb_mst and
enable bit, it wastes too manys times.

We can simple check the vop cfg_done register to sure vop register
take effect. when we have a new config, set cfg_done to 1, then the
cfg_done would auto clear at frame start event. So when cfg_done is
zero, means that there is no pending configs.

Change-Id: Ib87114cdaea4d3bbc23fd9e0bd9b49d02f4ae1e3
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>