msm: vidc: add driver support to enable operating rate

Add support for enabling operating rate in encoder. This will enable
support for high fps/timelapse recording and still maintain 30fps
timestamp deltas between two input frames.

Change-Id: I1f59db533b61e6f42d8b7768396057f6ec5b690d
Signed-off-by: Ashray Kulkarni <ashrayk@codeaurora.org>