dt-bindings: clk: sunxi-ccu: add compatible string for V3 CCU

Despite Allwinner V3 and V3s shares the same die, one peripheral (I2S)
is only available on V3, and thus the clocks is not declared for V3s
CCU.

Add a V3 CCU compatible string to the binding to prepare for a CCU
driver that provide I2S clock on V3, but not on V3s.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>