drm/msm/mdp5: Wait for PP_DONE irq for command mode CRTC atomic commit

CRTCs in DSI command mode data path should wait for pingpong done,
instead of vblank, to finish atomic commit.

This change is to enable PP_DONE irq on command mode CRTCs and wait for
this irq happens before atomic commit completion.

Signed-off-by: Hai Li <hali@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>