stm32: Convert serial driver to DM

Signed-off-by: Kamil Lulko <kamil.lulko@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 7383975..75d6bbc 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -697,6 +697,8 @@
 config TARGET_STM32F429_DISCOVERY
 	bool "Support STM32F429 Discovery"
 	select CPU_V7M
+	select DM
+	select DM_SERIAL
 
 config ARCH_ROCKCHIP
 	bool "Support Rockchip SoCs"