CONFIG_ARCH_EFM32 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Energy Micro efm32

modulename: clk-efm32gg.ko

configname: CONFIG_ARCH_EFM32

ARM system type
└─>Energy Micro efm32
In linux kernel since version 3.14 (release Date: 2014-03-30)  
Support for Energy Micro's (now Silicon Labs) efm32 Giant Gecko
processors.

source code:
drivers/clk/clk-efm32gg.c

depends
NOT CONFIG_MMU

is selected by
CONFIG_CLKSRC_EFM32