iommu/vt-d: Avoid unnecessary cache flush in pasid entry teardown

iommu/vt-d: Avoid unnecessary cache flush in pasid entry teardown

When a present pasid entry is disassembled, all kinds of pasid related
caches need to be flushed. But when a pasid entry is not being used
(PRESENT bit not set), we don't need to do this. Check the PRESENT bit
in intel_pasid_tear_down_entry() and avoid flushing caches if it's not
set.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20210320025415.641201-6-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>