Extend the scope of holding group->mutex so that it can cover the default
domain check/attachment and direct mappings of reserved regions.

Cc: Ashish Mhetre <amhetre@nvidia.com>
Fixes: 211ff31b ("iommu: Fix race condition during default domain allocation")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20211108061349.1985579-1-baolu.lu@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>