Uncache the active buffer slot last

This allows the memory for the active buffer to be freed as soon as
possible by purging it from HWC cache as soon as the next buffer is sent
to the layer.

Bug: 258196272
Test: atest OutputLayerUncacheBufferTest
Change-Id: I96c24390de5757ac99b369119e9ba031afb0b042
3 files changed