CONFIG_METAG_META21_MMU is not available for thedefaultarchitecture x86.
Result is shown for architecture metag
Meta 2.x MMU mode
configname: CONFIG_METAG_META21_MMU
Linux Kernel Configuration
└─>SoC configuration
└─>Meta 2.x MMU mode
In linux kernel since version 3.1 (release Date: 2011-10-24)
Use the Meta 2.x MMU in extended mode.