AGPS: Support basic AGPS configurations by user.

1. Add the function for user to config SUPL host and port.
2. User can set position mode for AGPS
3. When in roaming status, user can stop AGPS automatically.
4. User can set the start mode for cold, warm, hot. It will
clean the xtra info when starting in cold mode.

The first two features are controlled by resource
assisted_gps_configurable_list. If carrier open it in overlay,
these two functions can work.

Change-Id: I1e524c4cbf9da8a2535758aee79d62eeafa64808