dt-bindings: arm: amlogic: add Banana PI M5 bindings

Add bindings for the Banana PI M5 board.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210514143255.3352774-3-narmstrong@baylibre.com