ARM: dts: stm32: convert stm23f4 boards to OF_UPSTREAM

Enable OF_UPSTREAM flag for STM32MPF4 platforms.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/arch/arm/mach-stm32/Kconfig b/arch/arm/mach-stm32/Kconfig
index 031fb9a..de9d854 100644
--- a/arch/arm/mach-stm32/Kconfig
+++ b/arch/arm/mach-stm32/Kconfig
@@ -15,6 +15,7 @@
 	select STM32_SERIAL
 	select STM32_TIMER
 	select TIMER
+	imply OF_UPSTREAM
 
 config STM32F7
 	bool "stm32f7 family"