boards: frdm-mcxn947: Enable flexcomm3

Flexcomm3 is used for the mikrobus header, enable the clock for it and
setup a pinctrl group for i2c.

Signed-off-by: Tom Burdick <thomas.burdick@intel.com>

Author: teburd

boards/nxp/frdm_mcxn947/board.c

@@ -159,6 +159,12 @@ void board_early_init_hook(void)
 	CLOCK_AttachClk(kFRO_HF_DIV_to_FLEXCOMM2);
 #endif
 
+#if DT_NODE_HAS_STATUS_OKAY(DT_NODELABEL(flexcomm3))
+	/* Configure input clock to be able to reach the datasheet specified SPI band rate. */
+	CLOCK_SetClkDiv(kCLOCK_DivFlexcom3Clk, 1u);
+	CLOCK_AttachClk(kFRO_HF_DIV_to_FLEXCOMM3);
+#endif
+
 #if DT_NODE_HAS_STATUS_OKAY(DT_NODELABEL(flexcomm4))
 	/* Configure input clock to be able to reach the datasheet specified SPI band rate. */
 	CLOCK_SetClkDiv(kCLOCK_DivFlexcom4Clk, 1u);

boards/nxp/frdm_mcxn947/frdm_mcxn947-pinctrl.dtsi

@@ -31,6 +31,18 @@
 		};
 	};
 
+	pinmux_flexcomm3_lpi2c: pinmux_flexcomm3_lpi2c {
+		group0 {
+			pinmux = <FC3_P0_PIO1_0>,
+				<FC3_P1_PIO1_1>;
+			slew-rate = "fast";
+			drive-strength = "low";
+			input-enable;
+			bias-pull-up;
+			drive-open-drain;
+		};
+	};
+
 	pinmux_flexcomm7_lpi2c: pimux_flexcomm7_lpi2c {
 		group0 {
 			pinmux = <FC7_P0_PIO3_2>,