ARM: dts: stm32: Add vrefbuf support to stm32mp157c

stm32mp157c has vrefbuf regulator that can provide analog reference
voltage from 1500mV to 2500mV.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32mp157c.dtsi

@@ -450,6 +450,15 @@ rcc: rcc@50000000 {
 			#reset-cells = <1>;
 		};
 
+		vrefbuf: vrefbuf@50025000 {
+			compatible = "st,stm32-vrefbuf";
+			reg = <0x50025000 0x8>;
+			regulator-min-microvolt = <1500000>;
+			regulator-max-microvolt = <2500000>;
+			clocks = <&rcc VREF>;
+			status = "disabled";
+		};
+
 		usart1: serial@5c000000 {
 			compatible = "st,stm32h7-uart";
 			reg = <0x5c000000 0x400>;