vfio/pci: Pass eventfd context object through irqfd

Further avoid lookup of the context object by passing it through the
irqfd data field.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240401195406.3720453-3-alex.williamson@redhat.com


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