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

Support RealView(R) Platform Baseboard for Cortex(tm)-A8 platform

modulename: realview_pba8.ko

configname: CONFIG_MACH_REALVIEW_PBA8

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

source code:
arch/arm/mach-realview/realview_pba8.c