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>