CONFIG_SOC_AU1X00 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_SOC_AU1X00 (not configurable)

configname: CONFIG_SOC_AU1X00

Linux/MIPS Kernel Configuration
└─>SOC_AU1X00
In linux kernel since version 2.6.12  

is selected by
CONFIG_SMC91X