nrf7002ek: dts: Add pull down to SPI MISO GPIO pin

Add a pull down to SPI MISO GPIO pin on nRF5340DK to ensure the i/o pin
on the nrf7002 device is not floating when SPI is inactive.

Signed-off-by: Bansidhar Mangalwedhekar <bansidhar.mangalwedhekar@nordicsemi.no>

Author: bama-nordic

boards/shields/nrf7002ek/boards/nrf5340dk_nrf5340_cpuapp.overlay

@@ -13,3 +13,34 @@
 &gpio_fwd {
 	status = "disabled";
 };
+
+/*
+ * Override the default pinctrl settings for SPI4 when used with the nRF7002 EK
+ * to pull down the MISO line. This is needed to avoid floating inputs when
+ * the SPI4 is not used. The default pinctrl settings are defined in the
+ * nrf5340_cpuapp_common_pinctrl.dtsi file.
+ */
+&pinctrl {
+	spi4_default: spi4_default {
+		group1 {
+			psels = <NRF_PSEL(SPIM_SCK, 1, 15)>,
+				<NRF_PSEL(SPIM_MOSI, 1, 13)>;
+		};
+		group2 {
+			psels = <NRF_PSEL(SPIM_MISO, 1, 14)>;
+			bias-pull-down;
+		};
+	};
+
+	spi4_sleep: spi4_sleep {
+		group1 {
+			psels = <NRF_PSEL(SPIM_SCK, 1, 15)>,
+				<NRF_PSEL(SPIM_MOSI, 1, 13)>;
+		};
+		group2 {
+			psels = <NRF_PSEL(SPIM_MISO, 1, 14)>;
+			bias-pull-down;
+		};
+		low-power-enable;
+	};
+};