drm: Check crtc_state->enable rather than crtc->enabled in drm_plane_helper_check_state()

drm_plane_helper_check_state() is supposed to do things the atomic way,
so it should not be inspecting crtc->enabled. Rather we should be
looking at crtc_state->enable.

We have a slight complication due to drm_plane_helper_check_update()
reusing drm_plane_helper_check_state() for non-atomic drivers. Thus
we'll have to pass the crtc_state in manally and construct a fake
crtc_state in drm_plane_helper_check_update().

v2: Fix the WARNs about plane_state->crtc matching crtc_state->crtc

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171101201558.6059-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/mediatek/mtk_drm_plane.c

@@ -111,7 +111,7 @@ static int mtk_plane_atomic_check(struct drm_plane *plane,
 	clip.x2 = crtc_state->mode.hdisplay;
 	clip.y2 = crtc_state->mode.vdisplay;
 
-	return drm_plane_helper_check_state(state, &clip,
+	return drm_plane_helper_check_state(state, crtc_state, &clip,
 					    DRM_PLANE_HELPER_NO_SCALING,
 					    DRM_PLANE_HELPER_NO_SCALING,
 					    true, true);