google_charger: add new vtier for defender

Factor common stats code to google_bms and add 2 new tiers for
defender stats

Bug: 218802317
Test: checked tier stats
Signed-off-by: Prasanna Prapancham <[email protected]>
Change-Id: I24358399217b09eb0a537f1463be2c29381741c1
(cherry picked from commit 11a0a5c578027b7d722ba30e4ab6923ad598509a)
4 files changed