msm: vidc: Add support for setting I-frame period

Add support for the V4L2 standard control for setting I-frame period.
Thus far, we've only had support for setting the IDR-frame period.

Change-Id: I877ec596d9056dd24384718bcb397bc5b8e6eede
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>