Gingerbread - option to disable combo scan

Change-Id: I2bb7f268cd494aeed6a6723fa33244a31a06efaa

Hi guys,
DHD driver in older kernels does not have combo scan and Gingerbread wpa_supplicant uses combo scan by default. So the scan fails and no access points show in the list.
This chaage adds board config settings to disable combo scans in wpa_supplicant so it can work with older kernels.