CONFIG_ETRAX_RS485 is not available for thedefaultarchitecture x86.
Result is shown for architecture cris

RS-485 support

configname: CONFIG_ETRAX_RS485

Linux Kernel Configuration
└─>RS-485 support
In linux kernel since version 2.6.12  
Enables support for RS-485 serial communication. For a primer on
RS-485, see <http://en.wikipedia.org/wiki/Rs485>