usb: gadget: push all usb_composite_driver structs into __refdata

As it turns out, Sam's comment was better than I initially assumed. This
patch pushes as struct usb_composite_driver data structures into
__refdata section to avoid a section missmatch report from modpost
because the ->bind() can be marked __init. The only downside is that
modpost does not check between ->bind() and other member. However, it is
temporary.

Cc: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>