CONFIG_I2C_THUNDERX is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT

Cavium ThunderX I2C bus support

modulename: i2c-thunderx.ko

configname: CONFIG_I2C_THUNDERX

Linux Kernel Configuration
└─>Device Drivers
└─>I2C support
└─>I2C Hardware Bus support
└─>Cavium ThunderX I2C bus support
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Say yes if you want to support the I2C serial bus on Cavium
ThunderX SOC.

This driver can also be built as a module. If so, the module
will be called i2c-thunderx.

source code: