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

Add documentations and dt-bindings headers for the AO clock and reset
controller.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>