drivers/vfio: Support EEH error injection

The patch adds one more EEH sub-command (VFIO_EEH_PE_INJECT_ERR)
to inject the specified EEH error, which is represented by
(struct vfio_eeh_pe_err), to the indicated PE for testing purpose.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>