msm: camera: isp: For testgen disable camif on frame boundary

When testgen is used then we cannot gate the input testgen on a frame
boundary and then stop camif. In this case if camif is stopped
immediately then it causes hardware failures on next camif start.
To avoid these errors from hardware always stop camif on frame
boundary when testgen is used.

Change-Id: I4e8e58626e5e8bd8468f3d216eadb2b326a84f75
CRs-Fixed: 987962
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>