mm-video-v4l2: Add extended config to set instance priority

Enable priority as hinted by the client:
priority = 0 => real-time
         = 1 => non-realtime
Also add the OMX extension for priority and operating-rate.

Amended by Ashray Kulkarni <ashrayk@codeaurora.org>
Default sessions to non-realtime.

bug: 20131548
Change-Id: I37532404a4a3ab5647b3490c3e3ecba2ed604bbf
6 files changed