usb: gadget: uvc: add v4l2 enumeration api calls

This patch adds support to the v4l2 VIDIOCs for enum_format,
enum_framesizes and enum_frameintervals. This way, the userspace
application can use these VIDIOCS to query the via configfs exported
frame capabilities. With thes callbacks the userspace doesn't have to
bring its own configfs parser.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20220909221335.15033-4-m.grzeschik@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>