drm/sun4i: sun6i-drc: Support DRC on A31 and A31s

The A31 and A31s also have the DRC as part of the display pipeline.
As we know virtually nothing about them, just add compatible strings
for both SoCs to the stub driver.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt

@@ -64,6 +64,8 @@ adaptive backlight control.
 
 Required properties:
   - compatible: value must be one of:
+    * allwinner,sun6i-a31-drc
+    * allwinner,sun6i-a31s-drc
     * allwinner,sun8i-a33-drc
   - reg: base address and size of the memory-mapped region.
   - interrupts: interrupt associated to this IP

drivers/gpu/drm/sun4i/sun6i_drc.c

@@ -98,6 +98,8 @@ static int sun6i_drc_remove(struct platform_device *pdev)
 }
 
 static const struct of_device_id sun6i_drc_of_table[] = {
+	{ .compatible = "allwinner,sun6i-a31-drc" },
+	{ .compatible = "allwinner,sun6i-a31s-drc" },
 	{ .compatible = "allwinner,sun8i-a33-drc" },
 	{ }
 };