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

Thunder MAC interface driver (RGX)

modulename: thunder_xcv.ko

configname: CONFIG_THUNDER_NIC_RGX

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet driver support
└─>PCI support
└─>Thunder MAC interface driver (RGX)
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This driver supports configuring XCV block of RGX interface
present on CN81XX chip.

source code:
drivers/net/ethernet/cavium/thunder/thunder_xcv.c


is depended by
CONFIG_THUNDER_NIC_BGX