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

Microwatt SoC platform

configname: CONFIG_PPC_MICROWATT

Linux Kernel Configuration
└─>Microwatt SoC platform
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
This option enables support for FPGA-based Microwatt implementations.