ARM: dts: msm: Disable iommu test clients

Currently, we are observing system hang when writing to
SMR and S2CR registers. Disable test clients for kgsl
and apps from attaching to smmu temporarily until this
issue is fixed.

Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
Change-Id: I3a2edfb8863719d296c992f31956d2e5470ab1ad