Add support for inband ringing feature

* Change HFP init API so that the HFP feature bit field depends on
  whether in-band ringing is supported on the device
* Feature disabled by default unless system property enables it

Bug: 19171297
Test: mm -j 40, HFP regression test, testplans/82144
Change-Id: Ib8ba28ac6e70eb23b2a2ad11c5805793911a4e43