net: qmi_wwan: add a number of Dell devices

Dan writes:

"The Dell drivers use the same configuration for PIDs:

81A2: Dell Wireless 5806 Gobi(TM) 4G LTE Mobile Broadband Card
81A3: Dell Wireless 5570 HSPA+ (42Mbps) Mobile Broadband Card
81A4: Dell Wireless 5570e HSPA+ (42Mbps) Mobile Broadband Card
81A8: Dell Wireless 5808 Gobi(TM) 4G LTE Mobile Broadband Card
81A9: Dell Wireless 5808e Gobi(TM) 4G LTE Mobile Broadband Card

These devices are all clearly Sierra devices, but are also definitely
Gobi-based.  The A8 might be the MC7700/7710 and A9 is likely a MC7750.

>From DellGobi5kSetup.exe from the Dell drivers:

usbif0: serial/firmware loader?
usbif2: nmea
usbif3: modem/ppp
usbif8: net/QMI"

Reported-by: AceLan Kao <acelan.kao@canonical.com>
Reported-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>