msm: mdss: Unblock hist IOCTL when Partial Update is enabled

Currently driver has checks to ensure that partial update
feature and post-processing features are mutually exclusive.
This enforcement is done as follows:

1. CABL/SVI/AD features need settling time to go in disabled
state which also requires access to histogram block. So
termination of these features are handled in userspace in
accordance with their disabled state.

2. CT-HSIC needs to be blocked at driver itself. So blocking
PP IOCTL so that it can't program CSC block.

Change-Id: I0f90e0a7b686b684045f46df3716d9a92d55515f
Signed-off-by: Nitesh Gupta <niteshg@codeaurora.org>