sepolicy: msmnile_au: add support for wlan dynamic detect

Add script init.qcom.wlan.sh for wlan device detecting
during system booting up; and property 'ro.vendor.wlan.chip'
to indicate the current wlan device.
With the help of the two upon, the correct wlan driver
can be selected and loaded properly when there are
more than one wlan drivers.

CRs-Fixed: 2470141
Change-Id: I06a914eeecef49ab42fe93f692b532f636e94637