iommu/amd: Globally detect SNP support

Modify existing SNP feature check to use the helper function
check_feature_on_all_iommus() to ensure consistency among all IOMMUs.
Also report IOMMU SNP support information for each IOMMU.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20220713225651.20758-6-suravee.suthikulpanit@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>