drm/radeon: use mmu_interval_notifier_insert

drm/radeon: use mmu_interval_notifier_insert

The new API is an exact match for the needs of radeon.

For some reason radeon tries to remove overlapping ranges from the
interval tree, but interval trees (and mmu_interval_notifier_insert())
support overlapping ranges directly. Simply delete all this code.

Since this driver is missing a invalidate_range_end callback, but
still calls get_user_pages(), it cannot be correct against all races.

Link: https://lore.kernel.org/r/20191112202231.3856-8-jgg@ziepe.ca
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>