msm: mdss: Allow post-processing clean-up for primary display

Add checks to ensure that fb reset for post processing
features is done only for primary display.

Change-Id: Ied9381e7cbc22882d7d51e0470468f47fd548f32
Signed-off-by: Krishna Srinivas <krisrini@codeaurora.org>
Signed-off-by: Sravan Kumar D.V.N <sravank1@codeaurora.org>