msm: mdss: Move histogram completion initialization to pp_init

The histogram completion structure only needs to be initialized fully
once, and this can be done when the pp resource structure is created.
Otherwise, when enabling the histograms, it is sufficient to use the
reusable INIT_COMPLETION, in order to avoid any wait_queue errors.

Change-Id: Id4bfb19c91bd5ab07c01a5eb347ba50621fe8a97
Signed-off-by: Benet Clark <benetc@codeaurora.org>
Merge "msm: mdss: Move histogram completion initialization to pp_init"