telephony: IMS changes for VoLTE and VT

- Add IMS phone type constant
- Add system property persist.radio.calls.on.ims.
  It is set to true if VoLTE/VT calls are supported,
  false otherwise

Change-Id: I1296184fd70ea6da2adabdc35ad1d2fb25cdfc70
(cherry picked from commit b6b39f1792231aa435af56b16a5a5c53a50a3845)
(cherry picked from commit 69ac4a60fb230442c718dae44ccf44d2e5d41b7d)
(cherry picked from commit 2748954064ea4aef5b047668534d9332bd671e01)