serial: stm32: Use generic DT binding for announcing RTS/CTS lines

Add support of generic DT binding for annoucing RTS/CTS lines. The initial
binding 'st,hw-flow-control' is not needed anymore since generic binding
is available, but is kept for backward compatibility.

Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Link: https://lore.kernel.org/r/20200520133932.30441-3-erwan.leray@st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -1033,8 +1033,9 @@ static struct stm32_port *stm32_of_get_stm32_port(struct platform_device *pdev)
 	if (WARN_ON(id >= STM32_MAX_PORTS))
 		return NULL;
 
-	stm32_ports[id].hw_flow_control = of_property_read_bool(np,
-							"st,hw-flow-ctrl");
+	stm32_ports[id].hw_flow_control =
+		of_property_read_bool (np, "st,hw-flow-ctrl") /*deprecated*/ ||
+		of_property_read_bool (np, "uart-has-rtscts");
 	stm32_ports[id].port.line = id;
 	stm32_ports[id].cr1_irq = USART_CR1_RXNEIE;
 	stm32_ports[id].cr3_irq = 0;