ARM: dts: stm32f429: add LSI and LSE clocks

This patch adds lsi / lse oscillators. These clocks can be use by
RTC clocks.
The clock drivers needs to disable the power domain write protection using
syscon / regmap to enable these clocks.
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32f429.dtsi

@@ -56,6 +56,18 @@ clk_hse: clk-hse {
 			compatible = "fixed-clock";
 			clock-frequency = <0>;
 		};
+
+		clk-lse {
+			#clock-cells = <0>;
+			compatible = "fixed-clock";
+			clock-frequency = <32768>;
+		};
+
+		clk-lsi {
+			#clock-cells = <0>;
+			compatible = "fixed-clock";
+			clock-frequency = <32000>;
+		};
 	};
 
 	soc {
@@ -189,6 +201,11 @@ exti: interrupt-controller@40013c00 {
 			interrupts = <1>, <2>, <3>, <6>, <7>, <8>, <9>, <10>, <23>, <40>, <41>, <42>, <62>, <76>;
 		};
 
+		pwrcfg: power-config@40007000 {
+			compatible = "syscon";
+			reg = <0x40007000 0x400>;
+		};
+
 		pin-controller {
 			#address-cells = <1>;
 			#size-cells = <1>;
@@ -346,6 +363,7 @@ rcc: rcc@40023810 {
 			compatible = "st,stm32f42xx-rcc", "st,stm32-rcc";
 			reg = <0x40023800 0x400>;
 			clocks = <&clk_hse>;
+			st,syscfg = <&pwrcfg>;
 		};
 
 		dma1: dma-controller@40026000 {