x86/iommu: Correct a recent change to iommu_domain_unload_entry()

Correct 8bc367384745. When iommu_domain_unload_entry() performs a
synchronous IOTLB invalidation, it must call dmar_domain_free_entry()
to remove the entry from the domain's RB_TREE.

Push down the acquisition and release of the DMAR lock into the
recently introduced function dmar_qi_invalidate_sync_locked() and
remove the _locked suffix.

MFC with: 8bc367384745