Remove the interval tree in the driver and rely on the tree maintained by
the mmu_notifier for delivering mmu_notifier invalidation callbacks.

For some reason amdgpu has a very complicated arrangement where it tries
to prevent duplicate entries in the interval_tree, this is not necessary,
each amdgpu_bo can be its own stand alone entry. interval_tree already
allows duplicates and overlaps in the tree.

Also, there is no need to remove entries upon a release callback, the
mmu_interval API safely allows objects to remain registered beyond the
lifetime of the mm. The driver only has to stop touching the pages during
release.

Link: https://lore.kernel.org/r/20191112202231.3856-12-jgg@ziepe.caReviewed-by: NPhilip Yang <Philip.Yang@amd.com>
Tested-by: NPhilip Yang <Philip.Yang@amd.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>