stm32mp: handle SYSRESET

Add support of sysreset with generic driver "syscon-reboot"
provided by RCC, for U-boot and for SPL.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/dts/stm32mp157-u-boot.dtsi b/arch/arm/dts/stm32mp157-u-boot.dtsi
index 7a9a4ce..1eca802 100644
--- a/arch/arm/dts/stm32mp157-u-boot.dtsi
+++ b/arch/arm/dts/stm32mp157-u-boot.dtsi
@@ -72,6 +72,10 @@
 	u-boot,dm-pre-reloc;
 };
 
+&rcc_reboot {
+	u-boot,dm-pre-reloc;
+};
+
 &pinctrl {
 	u-boot,dm-pre-reloc;
 };