usb: gadget: move bitflags to the end of usb_gadget struct

This patch moves all bitflags to the end of usb_gadget struct in order
to improve readability.

Signed-off-by: David Cohen <david.a.cohen@linux.intel.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>