CONFIG_PPC64 is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

64-bit kernel

modulename: nvram.ko

and/or

setup-bus.ko

and/or

init_64.ko

and/or

checksum_64.ko

and/or

setup_64.ko

and/or

misc_64.ko

configname: CONFIG_PPC64

Linux Kernel Configuration
└─>64-bit kernel
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
This option selects whether a 32-bit or a 64-bit kernel
will be built.

source code:
arch/powerpc/platforms/powermac/nvram.c