dt-bindings: clock: reset: Add AXG AO Clock and Reset Bindings

Add dt-bindings headers for the Meson-AXG's AO clock and
reset controller.

Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>