dt-bindings: phy: sun4i-usb-phy: Add compatible string for A83T

The A83T has 3 USB PHYs, 1 for OTG, 1 for standard USB, 1 for USB HSIC.

Add a compatible string for it, and describe the needed properties.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>