Display signal strength on data-only SIMs.

On SIM cards that support data but not voice, we currently
display a null signal strength icon, which is confusing because
data is actually working.

Fix this by displaying signal bars as well as showing the
"emergency calls only" or "no service" text which indicates that
voice service is not available.

Bug: 3339315
Change-Id: I7d888721e8dc5e22fefd1b8fa85ba046d46a8fba