Telephony: Add isRadioOn() method

The implementation of ITelephony.isRadioOn() method checks for
service state instead of radio state. In cases of basebandless
targets, service state is not changed and would remain in the
initialized OUT_OF_SERVICE state. This causes delay in shutdown
procedure for such targets.

Hence a method isRadioOn() is added in phone interface to get
the radio state.

Change-Id: I33760b710a1ef5ba50b92a014c72f33d8dc5e782
CRs-Fixed: 502317
(cherry picked from commit 21554a64826befd6fbaa6e5d341d60b4722b2a6a)
(cherry picked from commit 512862bcca51fb58e0f2b6b32a6d335db6cf257c)
(cherry picked from commit 7042c2deb7dc0e235e453c887aa7596e6db1110e)