staging: r8188eu: Add files for new driver - part 20

This commit adds files os_dep/usb_intf.c, os_dep/usb_ops_linux.c,
and os_dep/xmit_linux.c.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>