MLK-17231-1: drm: imx: dcss: set own KMS commit_tail callback

MLK-17231-1: drm: imx: dcss: set own KMS commit_tail callback

According to documentation, for the default commit_tail helper:

 * Note that the default ordering of how the various stages are called is to
 * match the legacy modeset helper library closest. One peculiarity of that is
 * that it doesn't mesh well with runtime PM at all.
 *
 * For drivers supporting runtime PM the recommended sequence is instead ::
 *
 *     drm_atomic_helper_commit_modeset_disables(dev, state);
 *
 *     drm_atomic_helper_commit_modeset_enables(dev, state);
 *
 *     drm_atomic_helper_commit_planes(dev, state,
 *                                     DRM_PLANE_COMMIT_ACTIVE_ONLY);

This patch creates our own commit_tail() callback and changes the order of the
commit_modeset callbacks, as instructed.

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@nxp.com>