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

SDRAM support

configname: CONFIG_ETRAX_SDRAM

Linux Kernel Configuration
└─>CRIS v10 options
└─>SDRAM support
In linux kernel since version 2.6.12  
Enable this if you use SDRAM chips and configure
R_SDRAM_CONFIG and R_SDRAM_TIMING as well.