ARM: tegra: Register host1x node with IOMMU binding on Tegra124

This registers the host1x node with the SMMU (as HC swgroup) to allow
the host1x code to attach to it. It avoid failing the probe sequence,
which resulted in the Tegra DRM driver not probing and thus nothing
being displayed on-screen.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Thierry Reding <treding@nvidia.com>