CONFIG_LOONGSON_MC146818 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_LOONGSON_MC146818 (not configurable)

modulename: rtc.ko

configname: CONFIG_LOONGSON_MC146818

Linux Kernel Configuration
└─>LOONGSON_MC146818
In linux kernel since version 2.6.35 (release Date: 2010-08-01)  
source code:
arch/mips/loongson/common/rtc.c