drm/komeda: SW workaround for D71 doesn't flush shadow registers

This is a SW workaround for shadow un-flushed when together with the
DOU Timing-disable.

D71 HW doesn't update shadow registers when display output is turned
off. So when we disable all pipeline components together with display
output disabling by one flush or one operation, the disable operation
updated registers will not be flushed or valid in HW, which may lead
problem. To workaround this problem, introduce a two phase disable for
pipeline disable.

Phase1: Disable components with display is on and flush it, this phase
        for flushing or validating the shadow registers.
Phase2: Turn-off display output.

Signed-off-by: Lowry Li (Arm Technology China) <lowry.li@arm.com>
Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190906071750.4563-1-lowry.li@arm.com