dt-bindings: add compatible string for the A64 DE2 CCU

The Allwinner A64 SoC has a DE2 CCU like the one in the DE2 of Allwinner
H5 SoC.

Add a compatible string for it.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

Documentation/devicetree/bindings/clock/sun8i-de2.txt

@@ -6,6 +6,7 @@ Required properties :
 		- "allwinner,sun8i-a83t-de2-clk"
 		- "allwinner,sun8i-h3-de2-clk"
 		- "allwinner,sun8i-v3s-de2-clk"
+		- "allwinner,sun50i-a64-de2-clk"
 		- "allwinner,sun50i-h5-de2-clk"
 
 - reg: Must contain the registers base address and length