iommu/vt-d: Make unnecessarily global functions static

Make some functions static as they are only used inside pasid.c.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210323010600.678627-6-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>