Camera2: Fix ZSL bugs.

The ZSL processor was discarding buffers too often, and waiting for
new buffers with mutexes held.

Also adds basic fallback to regular capture in case the ZSL queue
doesn't contain a suitable buffer.

Bug: 7147043

Change-Id: I5721267ef08dbc87ef9d8ec47f333db5f67e41c1
3 files changed