CONFIG_ETRAX_SERIAL_PORT4 is not available for thedefaultarchitecture x86.
Result is shown for architecture cris
default or selected kernelversion does not have config value CONFIG_ETRAX_SERIAL_PORT4.
Result is shown for kernelversion 6.2.5

Serial port 4 enabled

configname: CONFIG_ETRAX_SERIAL_PORT4

Linux Kernel Configuration
└─>Serial port 4 enabled
In linux kernel since version 2.6.25 (release Date: 2008-04-16)  
Enables the ETRAX FS serial driver for ser4 (ttyS4).