Add to receive BTHF_CALL_STATE_DISCONNECTED at HFP

When the call is disconnected, the BTHF state is changed to IDLE and
SCO connection is disconnected before playing disconnect tone. So the
disconnect tone can't be sound from BTHS.

Add DISCONNECTED state for HFP and keep the state until disconnect tone
sounds from BT.

Test: manual - Checked whether the disconnect tone is sound from the BTHS
Bug: 69645337
Change-Id: Iec361649e7d9f233a63a9d8b32a5048a05104c94