default or selected kernelversion does not have config value CONFIG_ARM_AT91_ETHER.
Result is shown for kernelversion 6.5.1

AT91RM9200 Ethernet support

modulename: at91_ether.ko

configname: CONFIG_ARM_AT91_ETHER

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet driver support
└─>AT91RM9200 Ethernet support
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
If you wish to compile a kernel for the AT91RM9200 and enable
ethernet support, then you should always answer Y to this.

source code: