dt-bindings: usb: ehci: Add Allwinner A83t compatible

The A83t EHCI compatible was introduced in device trees, but it was
never documented.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210721140424.725744-37-maxime@cerno.tech


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>