serial: serial_stm32: Enable uart FIFO for STM32F7xx SoCs

Since commit 7b3b74d321 ("serial: serial_stm32: Enable overrun")
on STM32F7xx based boards, the first lines of serial output are
missing during boot (we no more see the U-Boot release version,
board model and DRAM size).

By enabling the uart FIFO on STM32F7, the complete U-boot log
can be sent correctly.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>

drivers/serial/serial_stm32.h

@@ -37,7 +37,7 @@ struct stm32_uart_info stm32f4_info = {
 struct stm32_uart_info stm32f7_info = {
 	.uart_enable_bit = 0,
 	.stm32f4 = false,
-	.has_fifo = false,
+	.has_fifo = true,
 };
 
 struct stm32_uart_info stm32h7_info = {