composer: Cache the active config index

Cache the active config index whenever HWC calls SetActiveConfig
API on the Display Interface. The cached active config index will
be read by VSync 2.4 callback, etc., which don't require a lock on
the draw cycle thread in Composer process.

CRs-Fixed: 2683410
Change-Id: Ia74d7fe8575ce1529ce77eef024bc76866402c80
2 files changed