mtd: st_spi_fsm: only build for ARM

COMPILE_TEST allows us to build this driver on other arch'es. But not
all arch'es have the right I/O accessors -- particularly, x86 is missing
readsl() and writesl().

So just restrict this driver to ARCH_STI. It's still buildable for a
multiplatform ARM kernel, so it can get decent compile coverage.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Lee Jones <lee.jones@linaro.org>

drivers/mtd/devices/Kconfig

@@ -212,7 +212,7 @@ config MTD_DOCG3
 
 config MTD_ST_SPI_FSM
 	tristate "ST Microelectronics SPI FSM Serial Flash Controller"
-	depends on ARCH_STI || COMPILE_TEST
+	depends on ARCH_STI
 	help
 	  This provides an MTD device driver for the ST Microelectronics
 	  SPI Fast Sequence Mode (FSM) Serial Flash Controller and support