Fix volte replacement rat querying updated config value.

Currently the loading of Carier config value is done only
after SIM status is LOADED, so any component querying for
config value before SIM status LOADED will get the default
config value. This is causing the issue when the network
mode is LTE, volte replacement rat is stored with incorrect
value.

Fix: In PhoneProxy, register the receiver for carrier config
change and reload the updated carrier config value to get the
correct volte replacement rat.

Change-Id: I357b1480eb0da99c9ce2da5aeb192767055f7851
CRs-Fixed: 891677