Rewrite of the s390 channel subsystem driver for the new driver model

The channel subsystem driver a.k.a s390 common I/O layer is the low level
driver for most device drivers on s390 systems. The old code is largely
unchanged from the initial linux-2.2 port and there is a lot of bitrot
on it.

In particular, concepts from the 2.5 driver model are implemented in a
completely different and more complicated way here.
This rewrite tries to get the driver ready for 2.6. The new interface is
not compatible to the old one but should be rather stable now unless
someone finds major flaws.

The 's390dyn' and 'chandev' interfaces have been removed entirely (yippii!)
and are replaced by hotplug and sysfs interfaces.

Authors: Arnd Bergmann <arndb@de.ibm.com>,
         Cornelia Huck <cohuck@de.ibm.com>,
         Martin Schwidefsky <schwidefsky@de.ibm.com>