msm: vidc: Use pre-computed frame delta values in WFD use case

In WFD use-case with frame skipping enabled, we wish to fool the core
into thinking that that the frames are coming at a consistent rate so
that we don't run into any issues with the core's rate control
mechanism.

Introduce a client-settable property that dictates what the timestamp
delta between any two frames might be.

Change-Id: Iea3f97879227b7932543d3449d311758dc4a2f59
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>