Per PCIe r5.0, sec 9.3.7.11, VFs must not implement the PRI Capability.  If
the PF implements PRI, it is shared by the VFs.  Since VFs don't have a PRI
Capability, pci_enable_pri() always failed, which caused IOMMU setup to
fail.

Update the PRI interfaces so for VFs they reflect the state of the PF PRI.

[bhelgaas: rebase without pri_cap caching, commit log]
Suggested-by: NAshok Raj <ashok.raj@intel.com>
Link: https://lore.kernel.org/r/b971e31f8695980da8e4a7f93e3b6a3edba3edaa.1567029860.git.sathyanarayanan.kuppuswamy@linux.intel.com
Link: https://lore.kernel.org/r/20190905193146.90250-2-helgaas@kernel.orgSigned-off-by: NKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Keith Busch <keith.busch@intel.com>