GPS Signal Quality added to BatteryStats

- GPS Signal Quality (Top four average CN0) added to Batterystats
(Aggregate + Historian)

- Added API to obtain Gps battery stats for power drain diagnostics.

BUG:38354997

Test: Manual
(https://docs.google.com/document/d/1X6g7HBZ80GA3KuqEYyQtD0WQRUnXN8nbCpf0G1HvzqY/edit?usp=sharing)

Change-Id: Ic23bfa758977bf0677f368f617b0c28196d2d0c1