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
frames .

Change-Id: I7d47492909d182815b39c5d5399b7f9a1b335eb6
Signed-off-by: Alok Kediya <kediya@codeaurora.org>