PerformanceManager : Keep in sync with low power mode

Fix edge cases such as :

1) Toggling to power save when plugged in (Should reject)
2) Plugging in to power while in power save should toggle to
   balanced.
3) Toggling from power save to anything else should disable
   low power mode (Orange system bars...etc)

CYNGNOS-786

Change-Id: If6a4c08843673a6d02c38c94ed44d36230c0cb81
(cherry picked from commit 34ff00c8)