usb serial: Add generic USB wwan support

The generic USB serial code is ill-suited for high-speed USB wwan devices,
resulting in the option driver. However, other non-option devices may also
gain similar benefits from not using the generic code. Factorise out the
non-option specific code from the option driver and make it available to
other users.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/serial/Kconfig b/drivers/usb/serial/Kconfig
index 5f777c2..e399efd 100644
--- a/drivers/usb/serial/Kconfig
+++ b/drivers/usb/serial/Kconfig
@@ -576,6 +576,9 @@
 	  To compile this driver as a module, choose M here: the
 	  module will be called keyspan_pda.
 
+config USB_SERIAL_WWAN
+	tristate
+
 config USB_SERIAL_OPTION
 	tristate "USB driver for GSM and CDMA modems"
 	help