default or selected kernelversion does not have config value CONFIG_MV643XX_ETH_2.
Result is shown for kernelversion 5.4.123

MV-643XX Port 2

configname: CONFIG_MV643XX_ETH_2

Linux Kernel Configuration
└─>Networking support
└─>Ethernet (1000 Mbit)
└─>MV-643XX Port 2
In linux kernel since version 2.6.12  
This enables support for Port 2 of the Marvell MV643XX Gigabit
Ethernet.