CONFIG_CPU_MIPS32_R5_XPA is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Extended Physical Addressing (XPA)

configname: CONFIG_CPU_MIPS32_R5_XPA

Linux Kernel Configuration
└─>CPU selection
└─>Extended Physical Addressing (XPA)
In linux kernel since version 4.1 (release Date: 2015-06-21)  
Choose this option if you want to enable the Extended Physical
Addressing (XPA) on your MIPS32 core (such as P5600 series). The
benefit is to increase physical addressing equal to or greater
than 40 bits. Note that this has the side effect of turning on
64-bit addressing which in turn makes the PTEs 64-bit in size.
If unsure, say 'N' here.