usb: gadget: function: move u_f.h to include/linux/usb/func_utils.h

We move the func_utils.h header to include/linux/usb to be
able to compile function drivers outside of the
drivers/usb/gadget/function directory.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20240116-ml-topic-u9p-v12-1-9a27de5160e0@pengutronix.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>