New carrier config enhanced_4g_lte_title_variant_int

Carriers requires that changing the title as "4G Calling" for Enhanced 4G LTE
Mode settings.
Using int as index of string array would more flexible for different carriers

Bug: 112676117
Test: Manual test, setting config to 0, 1 or -1 to change the index for
verifying different variant title of Enhanced 4G LTE Mode settings.

Change-Id: I5ce96969337bc291dea98d5a7b01e3c182926bd9