iommu/amd: Refactor amd_iommu_domain_enable_v2 to remove locking

iommu/amd: Refactor amd_iommu_domain_enable_v2 to remove locking

The current function to enable IOMMU v2 also lock the domain.
In order to reuse the same code in different code path, in which
the domain has already been locked, refactor the function to separate
the locking from the enabling logic.

Co-developed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20220825063939.8360-5-vasant.hegde@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>