ARM: dts: stm32: Add sleep pinmux for SPI1 pins_a on stm32mp15

Add a sleep mux option for the SPI1 pins_a mux.

This is used on the Phycore STM32MP1.
Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32mp15-pinctrl.dtsi

@@ -2657,6 +2657,14 @@ pins2 {
 		};
 	};
 
+	spi1_sleep_pins_a: spi1-sleep-0 {
+		pins {
+			pinmux = <STM32_PINMUX('Z', 0, ANALOG)>, /* SPI1_SCK */
+				 <STM32_PINMUX('Z', 1, ANALOG)>, /* SPI1_MISO */
+				 <STM32_PINMUX('Z', 2, ANALOG)>; /* SPI1_MOSI */
+		};
+	};
+
 	usart1_pins_b: usart1-1 {
 		pins1 {
 			pinmux = <STM32_PINMUX('Z', 7, AF7)>; /* USART1_TX */