CONFIG_8xx_CPU15 is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CPU15 Silicon Errata

configname: CONFIG_8xx_CPU15

Linux Kernel Configuration
└─>MPC8xx CPM Options
└─>CPU15 Silicon Errata
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
This enables a workaround for erratum CPU15 on MPC8xx chips.
This bug can cause incorrect code execution under certain
circumstances. This workaround adds some overhead (a TLB miss
every time execution crosses a page boundary), and you may wish
to disable it if you have worked around the bug in the compiler
(by not placing conditional branches or branches to LR or CTR
in the last word of a page, with a target of the last cache
line in the next page), or if you have used some other

If in doubt, say Y here.