Update bluetooth QS tile secondary text.

Only show detailed status when connected to exactly one device.
Otherwise show "X devices".
Also, listen for bluetooth profile service callbacks to initialize the
bluetooth device state after systemui crashes.

TODO: Update string to "X devices connected" after P

Change-Id: I99a3484c3dfa7eb0d6d8836336ebb84cbdaadbe5
Fixes: 76102598
Fixes: 77498698
Test: manual