iommu/vt-d: Select PCI_PRI for INTEL_IOMMU_SVM

Previously intel-iommu.c depended on CONFIG_AMD_IOMMU in an undesirable
way.  When CONFIG_INTEL_IOMMU_SVM=y, iommu_enable_dev_iotlb() calls PRI
interfaces (pci_reset_pri() and pci_enable_pri()), but those are only
implemented when CONFIG_PCI_PRI is enabled.

The INTEL_IOMMU_SVM Kconfig did nothing with PCI_PRI, but AMD_IOMMU selects
PCI_PRI.  So if AMD_IOMMU was enabled, intel-iommu.c got the full PRI
interfaces, but if AMD_IOMMU was not enabled, it got the PRI stubs.

Make the iommu_enable_dev_iotlb() behavior independent of AMD_IOMMU by
having INTEL_IOMMU_SVM select PCI_PRI so iommu_enable_dev_iotlb() always
uses the full implementations of PRI interfaces.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Joerg Roedel <jroedel@suse.de>
Acked-by: Joerg Roedel <jroedel@suse.de>