Add APIs to return max possible active phones.

This is first step towards reboot free single SIM to DSDS switch. As
getPhoneCount returns active phone count based on current configuration,
getMaxPhoneCount (subject to renaming) will return max possible active
phones(logical modems).

Bug: 141023026
Test: manual

Change-Id: Icc6e7da7c065eb3f72ec85a99ccc148639c574da
2 files changed