s390/pci: Documentation for zPCI

There are changes in the usage of PCI for the user:
 - new kernel parameter
 - modification of the way functions are enumerated

Let's document these.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
4 files changed