usb: gadget: FunctionFS: convert to new function interface with backward compatibility

This is required in order to integrate configfs support.
f_fs needs to be a separately compiled module and so it needs to use the new
interface.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

diff --cc drivers/usb/gadget/Kconfig
Simple merge

diff --cc drivers/usb/gadget/Makefile
Simple merge

diff --cc drivers/usb/gadget/f_fs.c
Simple merge

diff --cc drivers/usb/gadget/g_ffs.c
Simple merge

diff --cc drivers/usb/gadget/u_fs.h
Simple merge

diff --cc include/linux/usb/functionfs.h
Simple merge