usb: gadget: uvc: add V4L2 dependency

usb: gadget: uvc: add V4L2 dependency

Building the UVC gadget into the kernel fails to build when
CONFIG_VIDEO_V4L2 is a loadable module:

drivers/usb/gadget/function/usb_f_uvc.o: In function `uvc_function_ep0_complete':
uvc_configfs.c:(.text.uvc_function_ep0_complete+0x84): undefined reference to `v4l2_event_queue'
drivers/usb/gadget/function/usb_f_uvc.o: In function `uvc_function_disable':
uvc_configfs.c:(.text.uvc_function_disable+0x34): undefined reference to `v4l2_event_queue'

Adding a dependency in USB_CONFIGFS_F_UVC (which is a bool symbol)
make the 'select USB_F_UVC' statement turn the USB_F_UVC into 'm'
whenever CONFIG_VIDEO_V4L2=m too, avoiding the link failure.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>