iommu/amd: Set page size bitmap during V2 domain allocation

With the addition of the V2 page table support, the domain page size
bitmap needs to be set prior to iommu core setting up direct mappings
for reserved regions. When reserved regions are mapped, if this is not
done, it will be looking at the V1 page size bitmap when determining
the page size to use in iommu_pgsize(). When it gets into the actual
amd mapping code, a check of see if the page size is supported can
fail, because at that point it is checking it against the V2 page size
bitmap which only supports 4K, 2M, and 1G.

Add a check to __iommu_domain_alloc() to not override the
bitmap if it was already set by the iommu ops domain_alloc() code path.

Cc: Vasant Hegde <vasant.hegde@amd.com>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Joerg Roedel <joro@8bytes.org>
Fixes: 4db6c41f

 ("iommu/amd: Add support for using AMD IOMMU v2 page table for DMA-API")
Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Link: https://lore.kernel.org/r/20230404072742.1895252-1-jsnitsel@redhat.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>