dt-bindings: arm: amlogic: add X96-AIR bindings

Add board bindings for the Amediatech X96-AIR STB which ships with
model variants distiguished by Ethernet configuration: models using
an external Gigabit PHY have a -gbit suffix, while models using an
internal 10/100 PHY have no suffix.

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/20220112022713.25962-3-christianshewitt@gmail.com