Add a system property for geotz

Add a system property that can be used to enable the Geolocation Time
Zone Detection feature. Previously it was hardcoded.

$ adb shell setprop \
    persist.sys.location_time_zone_detection_feature_enabled 1

... and a reboot to turn it on.

Bug: 151304765
Test: build / boot / flip / manual test
Change-Id: If8aa682cde05c18058a09bfd34b75d7ba9e5e46e