drm/msm/mdp: Use atomic helper to set crtc property

Assign drm_atomic_helper_crtc_set_property helper to MDP4 and MDP5
crtcs' set_property ops. This replaces the custom funcs that
returned an error even for standard crtc properties.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rob Clark <robdclark@gmail.com>