dt-bindings: phy: Add Amlogic G12A USB2 PHY Bindings

Add the Amlogic G12A Family USB2 OTG PHY Bindings

The PHY can work in host or peripheral modes depending on it's position.
Configuration of the mode is part of the USBCTRL registers which are
outside of the PHY registers.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/meson-g12a-usb2-phy.txt

+* Amlogic G12A USB2 PHY binding
+
+Required properties:
+- compatible:	Should be "amlogic,meson-g12a-usb2-phy"
+- reg:		The base address and length of the registers
+- #phys-cells:	must be 0 (see phy-bindings.txt in this directory)
+- clocks:	a phandle to the clock of this PHY
+- clock-names:	must be "xtal"
+- resets:	a phandle to the reset line of this PHY
+- reset-names:	must be "phy"
+- phy-supply:	see phy-bindings.txt in this directory
+
+Example:
+	usb2_phy0: phy@36000 {
+		compatible = "amlogic,g12a-usb2-phy";
+		reg = <0x0 0x36000 0x0 0x2000>;
+		clocks = <&xtal>;
+		clock-names = "xtal";
+		resets = <&reset RESET_USB_PHY21>;
+		reset-names = "phy";
+		#phy-cells = <0>;
+	};