s390/pci: introduce clp_get_state

Code handling pci hotplug needs to determine the configuration
state of a pci function. Implement clp_get_state as a wrapper
for list pci functions.

Also change enum zpci_state to match the configuration state
values.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>