msm: mdss: when fb splash logo enabled do not attach iommu

If fb splash logo is enabled pan display gets called with
continuous splash enabled. IOMMU attach should not be called
in such a case as this will lead to IOMMU page faults.

Change-Id: I59ac704c6fd77a7e731db0b544338cac3b8e8fe6
Signed-off-by: Vineet Bajaj <vbajaj@codeaurora.org>