msm: camera: isp: For burst stream fix framedrop period and pattern

For burst streams the period and pattern was not not configured
properly for non 0 skip pattern. Also, there is no need to
set the period and pattern on every EPOCH, instead set it once
initially or if there is an update.

Change-Id: I0d148fc283f8dc8910fc8bde27a48d523ae3ac2c
CRs-Fixed: 861108
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>
Signed-off-by: Peter Liu <pingchie@codeaurora.org>