dt-bindings: fix the binding of Allwinner DE2 CCU of A83T and H3

The DE2 CCU is different on A83T and H3 -- the parent of the clocks on
A83T is PLL_DE but on H3 it's the DE module clock. This is not noticed
when I develop the DE2 CCU driver.

Fix the binding by using different compatibles for A83T and H3, adding
notes for the PLL_DE usage on A83T, and change the binding example's
compatible from A83T to H3 (as it specifies the DE module clock).

Fixes: ed74f8a8 ("dt-bindings: add binding for the Allwinner DE2 CCU")
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>