32-bit kernel on PPC64 supported?

[Marvin]

Hi,

while trying to cleanup some configs/makefiles for ppc64 I noticed, that 
CONFIG_POWER4 implies CONFIG_PPC64 and vice versa in all defconfigs.
So I want to boldly replace CONFIG_POWER4 by CONFIG_PPC64 - ugh.

However, there are some constructs like:

#ifndef CONFIG_PPC64
...
#ifdef CONFIG_POWER4
...
#endif
...
#endif /* CONFIG_PPC64 */

in which POWER4 is always undefined, e.g. in 
include/asm-powerpc/mmu_context.h. Maybe this is a leftover from times, where 
64-bit kernels where not supported on Powermacs. Is this 32-bit support still 
necessary?

Greetings

Marvin