Add OverlayBufferManager.

Add OverlayBufferManager.

We need to track life time of OverlayBuffer in various cases:
1) Ensure its available until the buffer is scanned out and
   is being displayed on screen.
2) Ensure its not destroyed if it's going to be re-used.

We dont have a central tracking place for all this which is
making it hard to ensure the buffers are alive. This patch
adds OverlayBufferManager which is responsible for creating
the buffers and deleting them when it's not in use.

Jira: IAHWC-46
Test: No visible tearing with apps on Linux.

Signed-off-by: Kalyan Kondapally <kalyan.kondapally@intel.com>