default or selected kernelversion does not have config value CONFIG_SERIAL_M32R_SIO_CONSOLE.
Result is shown for kernelversion 6.7-rc3

use SIO console

configname: CONFIG_SERIAL_M32R_SIO_CONSOLE

Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>Serial drivers
└─>use SIO console
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Say Y here if you want to support a serial console.

If you use an M3T-M32700UT or an OPSPUT platform,
please say also y for SERIAL_M32R_PLDSIO.