vfio/pci-core: Add capability for AtomicOp completer support

Test and enable PCIe AtomicOp completer support of various widths and
report via device-info capability to userspace.

Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Robin Voetter <robin@streamhpc.com>
Tested-by: Robin Voetter <robin@streamhpc.com>
Link: https://lore.kernel.org/r/20230519214748.402003-1-alex.williamson@redhat.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>