iommu/arm-smmu-qcom: Only enable stall on smmu-v2

On mmu-500, stall-on-fault seems to stall all context banks, causing the
GMU to misbehave.  So limit this feature to smmu-v2 for now.

This fixes an issue with an older mesa bug taking outo the system
because of GMU going off into the year.

https://lore.kernel.org/linux-iommu/CAF6AEGsFeibyH5_a7m=9PMKReD4Xb+c=dEGsbCN0_UHiJK1vbA@mail.gmail.com/T/#ma88e83db2e824a3834bda205391d36fe4de2d068



Signed-off-by: Rob Clark <robdclark@chromium.org>