CONFIG_AMIGA is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k

Amiga support

configname: CONFIG_AMIGA

Linux Kernel Configuration
└─>Amiga support
In linux kernel since version 2.6.12  
This option enables support for the Amiga series of computers. If
you plan to use this kernel on an Amiga, say Y here and browse the
material available in <file:Documentation/m68k>; otherwise say N.

selects
CONFIG_MMU_MOTOROLA
CONFIG_LEGACY_TIMER_TICK