arm64: dts: st: add spi3 / spi8 properties on stm32mp257f-ev1

Add properties for spi3 and spi8 available on the stm32mp257f-ev1.
Both are kept disabled since only used via the gpio expansion connector.
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm64/boot/dts/st/stm32mp257f-ev1.dts

@@ -88,6 +88,20 @@ &sdmmc1 {
 	status = "okay";
 };
 
+&spi3 {
+	pinctrl-names = "default", "sleep";
+	pinctrl-0 = <&spi3_pins_a>;
+	pinctrl-1 = <&spi3_sleep_pins_a>;
+	status = "disabled";
+};
+
+&spi8 {
+	pinctrl-names = "default", "sleep";
+	pinctrl-0 = <&spi8_pins_a>;
+	pinctrl-1 = <&spi8_sleep_pins_a>;
+	status = "disabled";
+};
+
 &usart2 {
 	pinctrl-names = "default", "idle", "sleep";
 	pinctrl-0 = <&usart2_pins_a>;