iommu/amd: Do not enable SNP when V2 page table is enabled

DTE[Mode]=0 is not supported when SNP is enabled in the host. That means
to support SNP, IOMMU must be configured with V1 page table (See IOMMU
spec [1] for the details). If user passes kernel command line to configure
IOMMU domains with v2 page table (amd_iommu=pgtbl_v2) then disable SNP
as the user asked by not forcing the page table to v1.

[1] https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/specifications/48882_IOMMU.pdf



Cc: Ashish Kalra <ashish.kalra@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240410085702.31869-1-vasant.hegde@amd.com


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