ARM: dts: stm32: Add u-boot, dm-pre-reloc for usart1_pins_a for stm32f769-disco

This allow to get console output in SPL for stm32f769-disco.
Signed-off-by: NPatrice Chotard <patrice.chotard@st.com>

arch/arm/dts/stm32f769-disco-u-boot.dtsi

@@ -152,6 +152,16 @@
 			slew-rate = <2>;
 		};
 	};
+
+	usart1_pins_a: usart1@0	{
+		u-boot,dm-pre-reloc;
+		pins1 {
+			u-boot,dm-pre-reloc;
+		};
+		pins2 {
+			u-boot,dm-pre-reloc;
+		};
+	};
 };
 
 &qspi {