dt-bindings: arm: amlogic: add support for Radxa Zero

Radxa Zero is a small form-factor SBC with an Amlogic S905Y2 chip.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20210909102154.22710-2-christianshewitt@gmail.com