usb: gadget: f_fs: Add compat_ioctl to epfiles

This allows 32 bit owners of ffs endpoints to
make ioctls into a 64 bit kernel.

All of the current epfile ioctls can be handled
with the same struct definitions as regular
ioctl.

Acked-by: Michał Nazarewicz <mina86@mina86.com>
Signed-off-by: Jerry Zhang <zhangjerry@google.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>