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 OMAP Common 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.

depends
CONFIG_ARCH_OMAP |
| CONFIG_ARCH_OMAP1

is selected by
CONFIG_SND_OMAP_SOC_N810