CONFIG_HAVE_AT91_I2S_MUX_CLK is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_HAVE_AT91_I2S_MUX_CLK (not configurable)

modulename: clk-i2s-mux.ko

configname: CONFIG_HAVE_AT91_I2S_MUX_CLK

Linux Kernel Configuration
└─>AT91/Microchip SoCs
└─>HAVE_AT91_I2S_MUX_CLK
In linux kernel since version 4.2 (release Date: 2015-08-30)  
source code:
drivers/clk/at91/clk-i2s-mux.c

is depended by
CONFIG_SOC_SAMA5D2