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/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index 91555c0..13ac2c5 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -454,10 +454,10 @@ int vmw_du_primary_plane_atomic_check(struct drm_plane *plane,
 		clip.y2 = crtc_state->adjusted_mode.vdisplay;
 	}
 
-	ret = drm_plane_helper_check_state(state, crtc_state, &clip,
-					   DRM_PLANE_HELPER_NO_SCALING,
-					   DRM_PLANE_HELPER_NO_SCALING,
-					   false, true);
+	ret = drm_atomic_helper_check_plane_state(state, crtc_state, &clip,
+						  DRM_PLANE_HELPER_NO_SCALING,
+						  DRM_PLANE_HELPER_NO_SCALING,
+						  false, true);
 
 	if (!ret && new_fb) {
 		struct drm_crtc *crtc = state->crtc;