msm: iommu: Revise GFX3D IOMMU contexts and M2V mappings

Based on recommendations from chip designers,
optimize the Machine ID to translation context
mappings for the 3D core's IOMMU. Remove the
the "gfx3d_smmu" context device, as it is no longer
needed under the new mapping scheme.

Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
[dwalker@codeaurora.org: updated commit text]
Signed-off-by: Daniel Walker <dwalker@codeaurora.org>