nubus: Add support for the driver model

This patch brings basic support for the Linux Driver Model to the
NuBus subsystem.

For flexibility, the matching of boards with drivers is left up to the
drivers. This is also the approach taken by NetBSD. A board may have
many functions, and drivers may have to consider many functional
resources and board resources in order to match a device.

This implementation does not bind drivers to resources (nor does it bind
many drivers to the same board). Apple's NuBus declaration ROM design
is flexible enough to allow that, but I don't see a need to support it
as we don't use the "slot zero" resources (in the main logic board ROM).

Eliminate the global nubus_boards linked list by rewriting the procfs
board iterator around bus_for_each_dev(). Hence the nubus device refcount
can be used to determine the lifespan of board objects.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>