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

Amiga builtin serial support

modulename: amiserial.ko

configname: CONFIG_AMIGA_BUILTIN_SERIAL

Linux Kernel Configuration
└─>Amiga builtin serial support
In linux kernel since version 2.6.12  
If you want to use your Amiga's built-in serial port in Linux,
answer Y.

To compile this driver as a module, choose M here.

depends
CONFIG_APUS