drm/msm/disp/dpu: reset the datapath after timing engine disable

Reset the datapath after disabling the timing gen, such that
it can start on a clean slate when the intf is enabled back.
This was a recommended sequence from the DPU HW programming guide.

Signed-off-by: Vinod Polimera <quic_vpolimer@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/524729/
Link: https://lore.kernel.org/r/1677774797-31063-8-git-send-email-quic_vpolimer@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>