dt-bindings: usb: generic-ehci: Add VIA/WonderMedia compatible

VIA/WonderMedia SoCs use a plain vanilla EHCI controller with a
compatible string "via,vt8500-ehci". This compatible is already
used by the mainline Linux driver and relevant in-tree DTS files,
so add it to the binding.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Alexey Charkov <alchark@gmail.com>
Link: https://lore.kernel.org/r/20250425-vt8500-ehci-binding-v2-1-b4a350335add@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>