nubus: Remove redundant code

Eliminate unused values from struct nubus_dev to save wasted memory
(a Radius PrecisionColor 24X card has about 95 functional resources
and up to six such cards may be fitted). Also remove redundant static
variable initialization, an unreachable !MACH_IS_MAC conditional,
the unused nubus_find_device() function, the bogus get_nubus_list()
prototype and the pointless card_present temporary variable.

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>