CONFIG_OMAP_MUX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

OMAP multiplexing support

configname: CONFIG_OMAP_MUX

Linux Kernel Configuration
└─>TI OMAP1
└─>TI OMAP1 specific features
└─>OMAP multiplexing support
In linux kernel since version 2.6.12  
Pin multiplexing support for OMAP boards. If your bootloader
sets the multiplexing correctly, say N. Otherwise, or if unsure,
say Y.