CONFIG_PPC_A2 is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_PPC_A2 (not configurable)

modulename: cpu_setup_a2.ko

configname: CONFIG_PPC_A2

Linux Kernel Configuration
└─>Processor support
└─>PPC_A2
In linux kernel since version 3 (release Date: 2011-07-21)  
source code:
arch/powerpc/kernel/