Show emc_only if modem reports emc_only

If modem reports emergency call only, then show the carrier text as
emergency call only, even though this carrier is not preferred when an
emergency call is made. The rationale is from user perspective, the
carrier text should reflect the carrier's coverage ability, not modem
implementatin.

Fix: 275695178
Test: reporter verified at 275695178#comment48
Change-Id: Ic1e3f68b2bf4b0c03a11390834acc5ecee25ef8a