CONFIG_FEC_LXT971 is not available for thedefaultarchitecture x86.
Result is shown for architecture ppc
default or selected kernelversion does not have config value CONFIG_FEC_LXT971.
Result is shown for kernelversion 5.4.123

Support LXT971 PHY

configname: CONFIG_FEC_LXT971

Linux Kernel Configuration
└─>MPC8xx CPM Options
└─>Support LXT971 PHY
In linux kernel since version 2.6.12