dt-bindings: usb: Convert Marvell Orion EHCI to DT schema

The Marvell Orion EHCI binding is just some compatible strings, so add it
to the generic-ehci.yaml schema.

Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/usb/ehci-orion.txt

···
-* EHCI controller, Orion Marvell variants
-
-Required properties:
-- compatible: must be one of the following
-	"marvell,orion-ehci"
-	"marvell,armada-3700-ehci"
-- reg: physical base address of the controller and length of memory mapped
-  region.
-- interrupts: The EHCI interrupt
-
-Optional properties:
-- clocks: reference to the clock
-- phys: reference to the USB PHY
-- phy-names: name of the USB PHY, should be "usb"
-
-Example:
-
-	ehci@50000 {
-		compatible = "marvell,orion-ehci";
-		reg = <0x50000 0x1000>;
-		interrupts = <19>;
-	};

Documentation/devicetree/bindings/usb/generic-ehci.yaml

···
           - const: usb-ehci
       - enum:
           - generic-ehci
+          - marvell,armada-3700-ehci
+          - marvell,orion-ehci
           - ti,ehci-omap
           - usb-ehci