CONFIG_ATH79_DEV_SPI is not available for the selected architecture x86.
Result is shown for architecture mips

CONFIG_ATH79_DEV_SPI (not configurable)

modulename: dev-spi.ko

configname: CONFIG_ATH79_DEV_SPI

Linux Kernel Configuration
└─>ATH79_DEV_SPI
In linux kernel since version 2.6.38 (release Date: 2011-03-14)
source code:
arch/mips/ath79/dev-spi.c
depends
CONFIG_ATH79

is depended by
CONFIG_ATH79_MACH_AP136