iommu/vt-d: Use real field for indication of first level

The dmar_domain uses bit field members to indicate the behaviors. Add
a bit field for using first level and remove the flags member to avoid
duplication.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20221118132451.114406-8-baolu.lu@linux.intel.com


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