dt-bindings: clock: sunxi-ccu: Add compatible string for A83T CCU

The A83T clock control unit is a hybrid of some new style clock designs
from the A80, and old style layout from the other Allwinner SoCs.

Like the A80, the SoC does not have a low speed 32.768 kHz oscillator.
Unlike the A80, there is no clock input either. The only low speed clock
available is the internal oscillator which runs at around 16 MHz,
divided by 512, yielding a low speed clock around 31.250 kHz.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>