ARM: dts: stm32mp1: DT alignment with Linux kernel v5.9-rc4

DT alignment with Linux kernel v5.9-rc4 for the STM32MP15x soc
device tree files and the STMicroelectronics boards device tree files.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/arch/arm/dts/stm32mp157a-dk1.dts b/arch/arm/dts/stm32mp157a-dk1.dts
index d03d4cd..4c8be9c 100644
--- a/arch/arm/dts/stm32mp157a-dk1.dts
+++ b/arch/arm/dts/stm32mp157a-dk1.dts
@@ -18,6 +18,8 @@
 	aliases {
 		ethernet0 = &ethernet0;
 		serial0 = &uart4;
+		serial1 = &usart3;
+		serial2 = &uart7;
 	};
 
 	chosen {