msm: camera: isp: Use epoch irq for SOF event

Send SOF event to userspace at EPOCH irq instead of at reg_update.
Reg_cmd is controlled by userspace. Do not auto program every
frame.

Change-Id: I54b302745b0a5d467d384e27ccc88b6285f94a23
Signed-off-by: Harsh Shah <harshs@codeaurora.org>
Signed-off-by: Sreesudhan Ramakrish Ramkumar <srramku@codeaurora.org>