feat(fdts stm32mp1): align DT with latest kernel

Update STM32MP1 device tree files with kernel 5.15.

Change-Id: Id405a79e18c61e80cd2292a4f87b7b9641df9c82
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/fdts/stm32mp157c-ev1.dts b/fdts/stm32mp157c-ev1.dts
index c5d12e3..4937514 100644
--- a/fdts/stm32mp157c-ev1.dts
+++ b/fdts/stm32mp157c-ev1.dts
@@ -57,6 +57,7 @@
 
 &usart3 {
 	pinctrl-names = "default";
-	pinctrl-0 = <&usart3_pins_a>;
+	pinctrl-0 = <&usart3_pins_b>;
+	uart-has-rtscts;
 	status = "disabled";
 };