dt-bindings: extcon: linux,extcon-usb-gpio: GPIO must be provided

Without providing either ID or VBUS GPIO the driver is not able to operate.
Original text binding says:
  "Either one of id-gpio or vbus-gpio must be present."

Fixes: 79a31ce0 ("dt-bindings: extcon: convert extcon-usb-gpio.txt to yaml format")
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Link: https://lore.kernel.org/lkml/20250904-yaml-extcon-usb-gpio-v2-1-a5c4afa496c3@ixit.cz/