drm/rockchip: Optimization vop mode set

Rk3288 vop timing registers is immediately register, when configure
timing on display active time, will cause tearing. use dclk reset is
not a good idea to avoid this tearing. we can avoid tearing by using
standby register.

Vop standby register will take effect at end of current frame, and
go back to work immediately when exit standby.

So we can use standby register to protect this context.

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