iommu/tegra-gart: Remove tegra-gart

Thierry says this is not used anymore, and doesn't think it makes sense as
an iommu driver. The HW it supports is about 10 years old now and newer HW
uses different IOMMU drivers.

As this is the only driver with a GART approach, and it doesn't really
meet the driver expectations from the IOMMU core, let's just remove it
so we don't have to think about how to make it fit in.

It has a number of identified problems:
 - The assignment of iommu_groups doesn't match the HW behavior

 - It claims to have an UNMANAGED domain but it is really an IDENTITY
   domain with a translation aperture. This is inconsistent with the core
   expectation for security sensitive operations

 - It doesn't implement a SW page table under struct iommu_domain so
   * It can't accept a map until the domain is attached
   * It forgets about all maps after the domain is detached
   * It doesn't clear the HW of maps once the domain is detached
     (made worse by having the wrong groups)

Cc: Thierry Reding <[email protected]>
Cc: Dmitry Osipenko <[email protected]>
Acked-by: Thierry Reding <[email protected]>
Reviewed-by: Lu Baolu <[email protected]>
Reviewed-by: Jerry Snitselaar <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>

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