msm: camera: isp: Add support to obtain frame index

This change captures the frame index as part of the IFE top
register space at every epoch event. The index is then notified
to userspace as part of shutter notification.

CRs-Fixed: 2524308
Change-Id: Iac510c452f9ceda86e9f7d69528f22f81e614974
Signed-off-by: Karthik Anantha Ram <kartanan@codeaurora.org>