USB: serial: qcserial: add EM9191 QDL support

When the module boots into QDL download mode it exposes the 1199:90d2
ids, which can be mapped to the qcserial driver, and used to run
firmware upgrades (e.g. with the qmi-firmware-update program).

  T:  Bus=01 Lev=03 Prnt=08 Port=03 Cnt=01 Dev#= 10 Spd=480 MxCh= 0
  D:  Ver= 2.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
  P:  Vendor=1199 ProdID=90d2 Rev=00.00
  S:  Manufacturer=Sierra Wireless, Incorporated
  S:  Product=Sierra Wireless EM9191
  S:  SerialNumber=8W0382004102A109
  C:  #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=2mA
  I:  If#=0x0 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=ff Prot=10 Driver=qcserial

Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>