Added carrier customized ETWS test channel support

Added carrier customized ETWS test channel support and changed
channel 0x802 and 0x804 on Softbank to ETWS test channel so it's
disabled by default unless users enable it.

Test: Manual and unit tests
bug: 69145050
Merged-In: I39d48d08f7aac9f601eaba8291176bff58bc4069
Change-Id: I39d48d08f7aac9f601eaba8291176bff58bc4069
(cherry picked from commit 5eb334ffb44b27ab76703a28f391e5008be9ad96)
(cherry picked from commit ea2d2d27eed836974112dcc8b5109461f6689a3b)
6 files changed