Add BLE results counter to batterystats

Batterystats provides an API to count the number of BLE scan results.

Bug: 37720787
Test: runtest -x frameworks/base/core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java
Change-Id: Idcb7494b39e88dcbfbb3da1ebe90b8a2f8f4d55c