dt-bindings: List devicetree binding for the CCU of Allwinner A20

Allwinner A20 is now driven by sunxi-ng CCU driver.

Add devicetree binding for it.
Acked-by: NRob Herring <robh@kernel.org>
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NPriit Laes <plaes@plaes.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

Documentation/devicetree/bindings/clock/sunxi-ccu.txt

@@ -6,6 +6,7 @@ Required properties :
 		- "allwinner,sun5i-a10s-ccu"
 		- "allwinner,sun5i-a13-ccu"
 		- "allwinner,sun6i-a31-ccu"
+		- "allwinner,sun7i-a20-ccu"
 		- "allwinner,sun8i-a23-ccu"
 		- "allwinner,sun8i-a33-ccu"
 		- "allwinner,sun8i-a83t-ccu"