msm: mdss: unmap buffers before starting Secure Display session

IOMMU will be detached for Secure Display session. We need to make
sure to unmap all the buffers before detaching IOMMU. There are a
couple of cases where the buffer on pipe which is being used for
Secure Display, isn't unmapped before IOMMU detach. Add handling
for such cases in validate and kickoff. Also, add changes to wait
for secure session completion in rotator, before mapping buffers.

Change-Id: Ia47f519b8ba471848bbf2eef4ae1c010f1d0c1d2
Signed-off-by: Krishna Chaitanya Devarakonda <kdevarak@codeaurora.org>