drm/sun4i: backend: Use explicit fourcc helpers for packed YUV422 check

Checking for the number of planes is not sufficient to en ensure that
the format is a packed YUV422.

Use explicit fourcc helpers for the check instead.
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190118145133.21281-4-paul.kocialkowski@bootlin.com

drivers/gpu/drm/sun4i/sun4i_backend.c

@@ -245,7 +245,8 @@ static int sun4i_backend_update_yuv_format(struct sun4i_backend *backend,
 			   SUN4I_BACKEND_ATTCTL_REG0_LAY_YUVEN);
 
 	/* TODO: Add support for the multi-planar YUV formats */
-	if (format->num_planes == 1)
+	if (drm_format_info_is_yuv_packed(format) &&
+	    drm_format_info_is_yuv_sampling_422(format))
 		val |= SUN4I_BACKEND_IYUVCTL_FBFMT_PACKED_YUV422;
 	else
 		DRM_DEBUG_DRIVER("Unsupported YUV format (0x%x)\n", fmt);