msm: camera: vfe: Add protection around list access

This change adds protection against concurrent access to free
event payload list in deinit bus hw routine. It also adds a
flag to store hardware init/deinit state that can be checked
before adding/removing event payloads from the free payload list.

Change-Id: Ie07455cdfa7568192eca682d1d0a5264701a4f26
Signed-off-by: Venkat Chinta <vchinta@codeaurora.org>