dt-bindings: usb: Convert Nuvoton EHCI to DT schema

The Nuvoton 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/generic-ehci.yaml

···
           - generic-ehci
           - marvell,armada-3700-ehci
           - marvell,orion-ehci
+          - nuvoton,npcm750-ehci
+          - nuvoton,npcm845-ehci
           - ti,ehci-omap
           - usb-ehci
 

Documentation/devicetree/bindings/usb/npcm7xx-usb.txt

···
-Nuvoton NPCM7XX SoC USB controllers:
------------------------------
-
-EHCI:
------
-
-Required properties:
-- compatible: should be one of
-    "nuvoton,npcm750-ehci"
-    "nuvoton,npcm845-ehci"
-- interrupts: Should contain the EHCI interrupt
-- reg:        Physical address and length of the register set for the device
-
-Example:
-
-	ehci1: usb@f0806000 {
-		compatible = "nuvoton,npcm750-ehci";
-		reg = <0xf0806000 0x1000>;
-		interrupts = <0 61 4>;
-	};