reset: meson: add dt-bindings for meson-axg audio arb

Add dt-bindings for the audio memory arbiter found on Amlogic's
A113 based SoCs

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