Update Null Cipher Enabled on Radio Available

Adds a new handling method on Phone that is overriden
by GsmCdmaPhone to handle requests for updates to the
SharedPreference that backs the null cipher enablement API.

The GsmCdmaPhone handles calling the handler on modem availability
which covers a reboot of the device or a restart of the modem after
crashes.

Test: atest GsmCdmaPhoneTest
Bug: 260844152
Change-Id: Ifaa70998d551c9fb7545211f725c51fad06ea80a