CONFIG_HAVE_AT91_H32MX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_HAVE_AT91_H32MX (not configurable)

modulename: clk-h32mx.ko

configname: CONFIG_HAVE_AT91_H32MX

Linux Kernel Configuration
└─>Atmel SoCs
└─>HAVE_AT91_H32MX
In linux kernel since version 3.18 (release Date: 2014-12-07)  
source code:
drivers/clk/at91/clk-h32mx.c

is depended by
CONFIG_SOC_SAMA5D4