DOWNSTREAM: drm/msm: use downstream iommu

Use downstream IOMMU driver for APQ8016.

MDP currently uses 3 different IOMMU drivers.

1) Downstream QCOM IOMMU driver -> For APQ8016
2) Upstream MSM IOMMU driver -> For APQ8064 and other 32 bit QCOM SoCs
3) Upstream ARM SMMU v2 driver -> For APQ8096

The downstream driver has iommu devices at a context (ctx) level,
and iommu_attach/detach_device require the context level device to
be passed. For this, there is a special msm_iommu_get_ctx API that
retrieves the ctx device by name. For other drivers, we just need
to use the iommu API normally, and pass mmu->dev.

Call the iommu_attach/detach according to what's needed.

Original patch by: Rob Clark <robdclark@gmail.com>

Signed-off-by: Archit Taneja <architt@codeaurora.org>