default or selected kernelversion does not have config value CONFIG_AU1000_UART.
Result is shown for kernelversion 5.15.113

Enable Au1000 UART Support

configname: CONFIG_AU1000_UART

Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>Enable Au1000 UART Support
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
If you have an Alchemy AU1000 processor (MIPS based) and you want
to use serial ports, say Y. Otherwise, say N.