ARM: DTS: stm32: add pwrcfg node for stm32f746

This node is needed to enable performance mode
when system frequency is set up to 200Mhz.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>
diff --git a/arch/arm/dts/stm32f7-u-boot.dtsi b/arch/arm/dts/stm32f7-u-boot.dtsi
index 5f77f57..a56ae93 100644
--- a/arch/arm/dts/stm32f7-u-boot.dtsi
+++ b/arch/arm/dts/stm32f7-u-boot.dtsi
@@ -22,3 +22,7 @@
 		 u-boot,dm-pre-reloc;
 	};
 };
+
+&pwrcfg {
+	u-boot,dm-pre-reloc;
+};