serial: stm32x7: add STM32F4 support

stm32f4 doesn't support FIFO and OVERRUN feature.
The enable bit is not at the same location in CR1
register than for STM32F7 and STM32H7.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 9bf2e26..7c54a49 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -531,9 +531,9 @@
 
 config STM32X7_SERIAL
 	bool "STMicroelectronics STM32 SoCs on-chip UART"
-	depends on DM_SERIAL && (STM32F7 || STM32H7)
+	depends on DM_SERIAL && (STM32F4 || STM32F7 || STM32H7)
 	help
-	  If you have a machine based on a STM32 F7 or H7 SoC you can
+	  If you have a machine based on a STM32 F4, F7 or H7 SoC you can
 	  enable its onboard serial ports, say Y to this option.
 	  If unsure, say N.