Add a device overlay for radio off delay due to IMS deregistration

Adds a new device overlay that allows a device to tune how long it
should wait for IMS deregistration in response to APM off or power
off indication. If 0, the feature should be disabled.

Bug: 195304068
Test: atest FrameworksTelephonyTests:ServiceStateTrackerTest
Change-Id: Id7b16d75c512106b56cb49974570811679498a0b