iommu/amd: Modify logic for checking GT and PPR features

iommu/amd: Modify logic for checking GT and PPR features

In order to support v2 page table, IOMMU driver need to check if the
hardware can support Guest Translation (GT) and Peripheral Page Request
(PPR) features. Currently, IOMMU driver uses global (amd_iommu_v2_present)
and per-iommu (struct amd_iommu.is_iommu_v2) variables to track the
features. There variables area redundant since we could simply just check
the global EFR mask.

Therefore, replace it with a helper function with appropriate name.

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/20230921092147.5930-10-vasant.hegde@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>