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

CONFIG_MMIO_NVRAM (not configurable)

modulename: mmio_nvram.ko

configname: CONFIG_MMIO_NVRAM

Linux/PowerPC Kernel Configuration
└─>Platform support
└─>MMIO_NVRAM
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
source code:
arch/powerpc/sysdev/mmio_nvram.c