CONFIG_MACH_REALVIEW_PBA8 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support RealView/PB-A8 platform

modulename: realview_pba8.ko

configname: CONFIG_MACH_REALVIEW_PBA8

Linux Kernel Configuration
└─>RealView platform type
└─>Support RealView/PB-A8 platform
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
Include support for the ARM(R) RealView Cortex-A8 Platform Baseboard.
PB-A8 is a platform with an on-board Cortex-A8 and has support for
PCI-E and Compact Flash.

source code: