iommu/amd: Implement device aquisition code for IOMMUv2

This patch adds the amd_iommu_init_device() and
amd_iommu_free_device() functions which make a device and
the IOMMU ready for IOMMUv2 usage.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>