MAINTAINERS: Update Tegra IOMMU maintainer

The email address for the Tegra IOMMU maintainer, Hiroshi, is no longer
valid. Hiroshi has not been maintaining the Tegra IOMMU driver for some
time now and so remove Hiroshi as the maintainer and add Thierry Reding
instead. Also add the mailing list information for this driver as well.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>