msm_fb: display: keep borderfill pipe's iommu info

Keep borderfill pipe's iommu info during base layer pipe
swap with original base layer pipe. Otherwise, borderfill
pipe's may contain original base layer pipe's iommu info
which cause iommu page fault due to same iommu buffer is
unmapped two times.

CRs-fixed: 436711
Change-Id: Ibdb792055287283c4449db07c2de2901aa4fe9b6
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>