vfio/pci: Support 8-byte PCI loads and stores

vfio/pci: Support 8-byte PCI loads and stores

Many PCI adapters can benefit or even require full 64bit read
and write access to their registers. In order to enable work on
user-space drivers for these devices add two new variations
vfio_pci_core_io{read|write}64 of the existing access methods
when the architecture supports 64-bit ioreads and iowrites.

Signed-off-by: Ben Segal <bpsegal@us.ibm.com>
Co-developed-by: Gerd Bayer <gbayer@linux.ibm.com>
Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
Link: https://lore.kernel.org/r/20240619115847.1344875-3-gbayer@linux.ibm.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>