boards: add zephyr_udc0 nodelabel to stm32 boards with usbotg_fs node

Add zephyr_udc0 (USB device controller) nodelabel to
STM32 boards with usbotg_fs node to allow generic USB device
samples to be build.

Follow up on commit e4f89478
("boards: add zephyr_udc0 nodelabel to all boards with USB support")

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>