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

CONFIG_PPC_DOORBELL (not configurable)

modulename: dbell.ko

configname: CONFIG_PPC_DOORBELL

Linux Kernel Configuration
└─>Processor support
└─>PPC_DOORBELL
In linux kernel since version 3.1 (release Date: 2011-10-24)  
source code:
arch/powerpc/kernel/dbell.c