USB: add siemens_mpi usb-serial "stub" driver

This driver got rescued from a few years ago and was requested to be
added.  So I cleaned it up, ported it to the latest kernel version and
here it is.

Cc: Thomas Hergenhahn <thomas.hergenhahn@suse.de>
Cc: Emmanuele <iemmav@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/Makefile

@@ -46,6 +46,7 @@ obj-$(CONFIG_USB_SERIAL_OPTION)			+= option.o
 obj-$(CONFIG_USB_SERIAL_OTI6858)		+= oti6858.o
 obj-$(CONFIG_USB_SERIAL_PL2303)			+= pl2303.o
 obj-$(CONFIG_USB_SERIAL_SAFE)			+= safe_serial.o
+obj-$(CONFIG_USB_SERIAL_SIEMENS_MPI)		+= siemens_mpi.o
 obj-$(CONFIG_USB_SERIAL_SIERRAWIRELESS)		+= sierra.o
 obj-$(CONFIG_USB_SERIAL_SPCP8X5)		+= spcp8x5.o
 obj-$(CONFIG_USB_SERIAL_TI)			+= ti_usb_3410_5052.o