msm: camera: isp: Improve flush handle in the IFE driver

A race condition between the flush operation and the IRQ handling has
been observed. The current flush implementation will cause a request
missing match between the IFE driver and CRM. This change add a new
flush state to handle the race condition correctly.

Change-Id: I8cb7137425d7f6bde6723d734efbbb01145336cc
Signed-off-by: Jing Zhou <jzhou70@codeaurora.org>