ARM: Kconfig: Select clocksource in STM32 entry

STM32 clocksource driver needs to be selected if ARCH_STM32.

Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0d4eb0e..72c4273 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -978,6 +978,7 @@
 	depends on ARM_SINGLE_ARMV7M
 	select ARCH_HAS_RESET_CONTROLLER
 	select ARMV7M_SYSTICK
+	select CLKSRC_STM32
 	select RESET_CONTROLLER
 	help
 	  Support for STMicroelectronics STM32 processors.