drm: Move drm_plane_helper_check_state() into drm_atomic_helper.c

drm_plane_helper_check_update() isn't a transitional helper, so let's
rename it to drm_atomic_helper_check_plane_state() and move it into
drm_atomic_helper.c.

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

Cc: Daniel Vetter <daniel@ffwll.ch>
Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171101201619.6175-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
index 08b899f..91919d5 100644
--- a/drivers/gpu/drm/tegra/dc.c
+++ b/drivers/gpu/drm/tegra/dc.c
@@ -500,8 +500,8 @@ static int tegra_plane_state_add(struct tegra_plane *plane,
 	clip.y2 = crtc_state->mode.vdisplay;
 
 	/* Check plane state for visibility and calculate clipping bounds */
-	err = drm_plane_helper_check_state(state, crtc_state, &clip,
-					   0, INT_MAX, true, true);
+	err = drm_atomic_helper_check_plane_state(state, crtc_state, &clip,
+						  0, INT_MAX, true, true);
 	if (err < 0)
 		return err;