clk: sunxi-ng: add support for DE2 CCU

The "Display Engine 2.0" in Allwinner newer SoCs contains a clock
management unit for its subunits, like the DE CCU in A80.

Add a sunxi-ng style driver for it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>