default or selected kernelversion does not have config value CONFIG_CRYPTO_DEV_LOONGSON_RNG.
Result is shown for kernelversion 6.18-rc7

Support for Loongson RNG Driver

modulename: loongson-rng.ko

configname: CONFIG_CRYPTO_DEV_LOONGSON_RNG

Linux Kernel Configuration
└─>Cryptographic API
└─>Hardware crypto devices
└─>Support for Loongson RNG Driver
In linux kernel since version 6.12.57 (release Date: 2025-11-02)  
Support for Loongson RNG Driver.

source code:
drivers/crypto/loongson/loongson-rng.c