iommu/amd: Use BUS_NOTIFY_REMOVED_DEVICE

Use the new device-notifier event instead of the old
BUS_NOTIFY_DEL_DEVICE to make sure the device driver had a
chance to uninit the device before all its mappings are
teared down.

Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>