dt-bindings: arm: amlogic: add libretech aml-s805x-ac bindings

Add bindings for the Libretech aml-s805x-ac board, aka 'La Frite'.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>