subsys: usb_device: Fix removal of board.h
subsys: usb_device: Fix removal of board.h

Restore including board.h to get USB_VUSB_EN_GPIO and associate defines
if the board.h sets them.  This should move to device tree in the
future.

Signed-off-by: Kumar Gala <a5e5248af4cd4f0ed8c515f61d40a6e2db46a66e@linaro.org>

galak/zephyr,punitvara/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,ldts/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,explora26/zephyr,nashif/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,ldts/zephyr,Vudentz/zephyr,finikorg/zephyr,ldts/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,explora26/zephyr,galak/zephyr,Vudentz/zephyr,punitvara/zephyr,explora26/zephyr,explora26/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,explora26/zephyr