msm: mdss: Unblock PP and hist ioctls when PU is enabled

Currently driver has checks to ensure that partial update feature
and post-processing feature are mutually exclusive. Ideally, this
enforcement should be done by clients of PP driver. This patch
removes all the partial update status checks for PP ioctls.

Change-Id: I0e50c16c3647dcebdf2eff37c632e554cc51002b
Signed-off-by: Ping Li <pingli@codeaurora.org>