mm-video-v4l2: venc: Add a utility to modify/access HAL1 meta-buffer

Extract the utility methods to access/modify fds/ints in
meta-buffer payload from BatchInfo class and move to an external
class.
This provides for a common and uniform way to access the
meta-buffer-payload for all clients (omx-venc, camera-HAL1 and
framework-extensions).
Furthermore, generalize the access for batch and non-batch mode
in omx-venc by using these utility methods.

CRs-Fixed: 1083833
Change-Id: I6eb4f8061d1eec309bfec2c25ee9d368620050d6
5 files changed