s390x/pci: change the device array to a list

In order to support a greater number of devices we use a QTAILQ
list of devices instead of a limited array.

This leads us to change:
- every lookup function s390_pci_find_xxx() for QTAILQ
- the FH_MASK_INDEX to index up to 65536 devices

Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
