dt-bindings: usb: gpio-sbu-mux: Make 'mode-switch' not required

On a i.MX8QXP MEK board that has an NXP CBDTU02043 mux, there is
no mode-switch support, only orientation switch.

Make the 'mode-switch' property a non-required one.
Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20231016131141.680517-1-festevam@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/gpio-sbu-mux.yaml

@@ -51,7 +51,6 @@ required:
   - compatible
   - enable-gpios
   - select-gpios
-  - mode-switch
   - orientation-switch
   - port