default or selected kernelversion does not have config value CONFIG_AU1000_UART.
Result is shown for kernelversion 5.15.5

Enable Au1000 UART Support

configname: CONFIG_AU1000_UART

Linux Kernel Configuration
└─> Device Drivers
└─> Character devices
└─> Enable Au1000 UART Support

If you have an Alchemy AU1000 processor (MIPS based) and you want
to use serial ports, say Y. Otherwise, say N.