This patch adds support for MF871A USB modem (aka Speed USB STICK U03)
to option driver. This modem is manufactured by ZTE corporation, and
sold by KDDI.

Interface layout:
0: AT
1: MODEM

usb-devices output:
T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  9 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=19d2 ProdID=1481 Rev=52.87
S:  Manufacturer=ZTE,Incorporated
S:  Product=ZTE Technologies MSM
S:  SerialNumber=1234567890ABCDEF
C:  #Ifs= 2 Cfg#= 1 Atr=80 MxPwr=500mA
I:  If#= 0 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=00 Driver=option
I:  If#= 1 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=00 Driver=option
Co-developed-by: Hiroyuki Yamamoto <hyamamo@allied-telesis.co.jp>
Signed-off-by: Hiroyuki Yamamoto <hyamamo@allied-telesis.co.jp>
Signed-off-by: Yoshiaki Okamoto <yokamoto@allied-telesis.co.jp>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>