CONFIG_MACH_CNS3420VB is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_MACH_CNS3420VB.
Result is shown for kernelversion 6.9.9

Support for CNS3420 Validation Board

configname: CONFIG_MACH_CNS3420VB

Linux Kernel Configuration
└─>Cavium Networks CNS3XXX family
└─>Support for CNS3420 Validation Board
In linux kernel since version 2.6.35 (release Date: 2010-08-01)  
Include support for the Cavium Networks CNS3420 MPCore Platform
Baseboard.
This is a platform with an on-board ARM11 MPCore and has support
for USB, USB-OTG, MMC/SD/SDIO, SATA, PCI-E, etc.