iommu/vt-d: Use iommu_sva_alloc(free)_pasid() helpers

Align the pasid alloc/free code with the generic helpers defined in the
iommu core. This also refactored the SVA binding code to improve the
readability.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20210520031531.712333-1-baolu.lu@linux.intel.com
Link: https://lore.kernel.org/r/20210610020115.1637656-8-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>