Telephony plumbing for SIM call manager voice status

For now, we add to GsmCdmaPhone's ServiceState merging logic, which is
already where IMS registration state is folded into the voice service
state value. This will be propagated to downstream callers via the
regular ServiceState and TelephonyCallback.ServiceStateListener APIs.

Bug: 205737545
Test: atest GsmCdmaPhoneTest
Change-Id: Ie5967eb0dfb3e19cf60156740434e76c1794af4b