dt-bindings: usb: new ehci-npcm7xx dt

Device Tree documentation for Nuvoton npcm7xx EHCI.

Signed-off-by: Avi Fishman <AviFishman70@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>