iommu/vt-d: Remove struct intel_svm

The struct intel_svm was used for keeping attached devices info for sva
domain. Since sva domain is a kind of iommu_domain, the struct
dmar_domain should centralize all info of a sva domain, including the
info of attached devices. Therefore, retire struct intel_svm and clean up
the code.

Besides, register mmu notifier callback  in domain_alloc_sva() callback
which allows the memory management notifier lifetime to follow the lifetime
of the iommu_domain. Call mmu_notifier_put() in the domain free and defer
the real free to the mmu free_notifier callback.

Co-developed-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240416080656.60968-13-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>