iommu/amd: Introduce helper functions for managing GCR3 table

Refactor domain_enable_v2() into helper functions for managing GCR3 table
(i.e. setup_gcr3_table() and get_gcr3_levels()), which will be used in
subsequent patches. Also re-arrange code and remove forward declaration.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Co-developed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Link: https://lore.kernel.org/r/20230921092147.5930-6-vasant.hegde@amd.com


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