powerpc/eeh: EEH device for VF

VFs and their corresponding pdn are created and released dynamically
when their PF's SRIOV capability is enabled and disabled. This creates
and releases EEH devices for VFs when creating and releasing their pdn
instances, which means EEH devices and pdn instances have same life
cycle. Also, VF's EEH device is identified by (struct eeh_dev::physfn).

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Acked-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>