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>

drivers/serial/Kconfig

@@ -531,9 +531,9 @@ config STI_ASC_SERIAL
 
 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.
 

drivers/serial/serial_stm32x7.c

@@ -127,6 +127,7 @@ static int stm32_serial_probe(struct udevice *dev)
 
 #if CONFIG_IS_ENABLED(OF_CONTROL)
 static const struct udevice_id stm32_serial_id[] = {
+	{ .compatible = "st,stm32-uart", .data = (ulong)&stm32f4_info},
 	{ .compatible = "st,stm32f7-uart", .data = (ulong)&stm32f7_info},
 	{ .compatible = "st,stm32h7-uart", .data = (ulong)&stm32h7_info},
 	{}

drivers/serial/serial_stm32x7.h

@@ -27,6 +27,13 @@ struct stm32_uart_info {
 	bool has_fifo;
 };
 
+struct stm32_uart_info stm32f4_info = {
+	.stm32f4 = true,
+	.uart_enable_bit = 13,
+	.has_overrun_disable = false,
+	.has_fifo = false,
+};
+
 struct stm32_uart_info stm32f7_info = {
 	.uart_enable_bit = 0,
 	.stm32f4 = false,