CellularTile shows Name of data carrier

The tile only controls the default data subscription (this is enforced
by using DataUsageController#setMobileDataEnabled). The secondary text
shows the carrier name when data is enabled.

Bug: 113343186
Test: manual with only one SIM and using DSDS
Change-Id: I1b8f0720618cd5b1679e1185e77d36b0227b663c