drm/vc4: Add comments for which HVS_PIXEL_ORDER_xxx defines apply

The HVS_PIXEL_ORDER_xxx defines apply to specific HVS_PIXEL_FORMAT_xxx
modes, so add comments to make this obvious.
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20221207-rpi-hvs-crtc-misc-v1-12-1f8e0770798b@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/vc4_regs.h

@@ -848,16 +848,19 @@ enum hvs_pixel_format {
 /* Note: the LSB is the rightmost character shown.  Only valid for
  * HVS_PIXEL_FORMAT_RGB8888, not RGB888.
  */
+/* For modes 332, 4444, 555, 5551, 6666, 8888, 10:10:10:2 */
 #define HVS_PIXEL_ORDER_RGBA			0
 #define HVS_PIXEL_ORDER_BGRA			1
 #define HVS_PIXEL_ORDER_ARGB			2
 #define HVS_PIXEL_ORDER_ABGR			3
 
+/* For modes 666 and 888 (4 & 5) */
 #define HVS_PIXEL_ORDER_XBRG			0
 #define HVS_PIXEL_ORDER_XRBG			1
 #define HVS_PIXEL_ORDER_XRGB			2
 #define HVS_PIXEL_ORDER_XBGR			3
 
+/* For YCbCr modes (8-12, and 17) */
 #define HVS_PIXEL_ORDER_XYCBCR			0
 #define HVS_PIXEL_ORDER_XYCRCB			1
 #define HVS_PIXEL_ORDER_YXCBCR			2