Camera: Handle onBuffersDiscarded callback

Use onBuffersDiscarded callback from buffer queue to invalidate the
buffer caches in cameraserver process.

Test: Run testDiscardFreeBuffers, and use trace to profile memory
Bug: 136677409
Bug: 145617243
Change-Id: Ifac5e852e2a1ac50f5c3f2e047966c59eeb5f1ba
Merged-In: Ifac5e852e2a1ac50f5c3f2e047966c59eeb5f1ba
(cherry picked from commit 0160ddd149893fd14c563ac9a124e49443b69fe4)