mm-video-v4l2:add extension to support av-timer

mm-video-v4l2: venc: add extension to support av-timer timestamps
Use timestamps sent in-band with graphic handles (updated from
camera with av-timer source) for vt usecases.

Bug: 32746650
Change-Id: I2bfb7215ca4446fecf6b5450aa40e4e26350846b
CRs-Fixed: 2026950