GpsLocationProvider: look for config file in /etc/gps.<ro.hardware.gps>.conf

The property ro.hardware.gps can be specifid to allow a single system
image to work with differrent GPS chips.  The HAL layer will use it to load
/system/lib/hw/gps.<ro.hardware.gps>.so.  Add support to GpsLocationProvider
to use the same property to find /etc/gps.<ro.hardware.gps>.conf, falling
back to /etc/gps.conf if the property is not set or the file is not present.

Change-Id: Ib285c4d28b0d0be5e038a1e61822edd8bc6d97d9