Refactor Cdma preference in ECM

When phone is in ECM mode and Cdma preference is clicked, it should
first pop up ECM exit dialog. If user click yes, then it should launch
normal dialog.

This CL create a Cdma preference to stop launch normal dialog when in
ECM mode.

Bug: 114749736
Test: RunSettingsRoboTests
Change-Id: Iba887d9fc49770b21cf0421ecc0120d63da43ef9