net: qmi_wwan: add Option GTM681W

[ Upstream commit aa3aba1cbcbe823bba623c7cab33d84ddf0fb6cd ]

A standard Gobi 3000 reference design module.

Reported-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>