msm: mdss: Fix compilation errors for MDP3 driver

Fix compilation errors for MDP3 with SMMU changes and remove
deprecated iommu references. Align to mdss sync functionalities
in place of software sync and also calculate threshold value to
create fences.
 
Change-Id: I06bdff45d69f598dfb9cc79eb29651a7766d407f
Signed-off-by: Arun kumar <akanak@codeaurora.org>