ARM: dts: stm32: enable RTC on stm32f429-disco

This patch enables RTC on stm32f429-disco with LSI as clock source because
X2 crystal for LSE is not fitted by default.
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32f429-disco.dts

@@ -94,6 +94,12 @@ &clk_hse {
 	clock-frequency = <8000000>;
 };
 
+&rtc {
+	assigned-clocks = <&rcc 1 CLK_RTC>;
+	assigned-clock-parents = <&rcc 1 CLK_LSI>;
+	status = "okay";
+};
+
 &usart1 {
 	pinctrl-0 = <&usart1_pins_a>;
 	pinctrl-names = "default";