drm/amd/display: Get rid of get_dm_commit_action

Use drm_atomic_crtc_needs_modeset instead.

Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>