boards: mimxrt1060: add lpuart8 pinctrl nodes for RT1060

The lpuart8 pinctrl nodes for RT1060 need to be defined, as WIFI + BT
(bt_tester) scenario requires three uart.
- LPUART1: shell uart
- LPUART3: bt hci uart
- LPUART8: uart pipe

Signed-off-by: Gang Li <gang.li_1@nxp.com>

Author: gangli02

boards/nxp/mimxrt1060_evk/mimxrt1060_evk-pinctrl.dtsi

@@ -21,7 +21,7 @@
 		};
 	};
 
-	/* conflicts with lpuart3 */
+	/* conflicts with lpuart3 and lpuart8 */
 	pinmux_csi: pinmux_csi {
 		group0 {
 			pinmux = <&iomuxc_gpio_ad_b0_04_gpio1_io04>;
@@ -302,6 +302,33 @@
 		};
 	};
 
+	pinmux_lpuart8: pinmux_lpuart8 {
+		group0 {
+			pinmux = <&iomuxc_gpio_ad_b1_11_lpuart8_rx>,
+				<&iomuxc_gpio_ad_b1_10_lpuart8_tx>;
+			drive-strength = "r0-6";
+			slew-rate = "slow";
+			nxp,speed = "100-mhz";
+		};
+	};
+
+	pinmux_lpuart8_sleep: pinmux_lpuart8_sleep {
+		group0 {
+			pinmux = <&iomuxc_gpio_ad_b1_11_gpio1_io27>;
+			drive-strength = "r0";
+			bias-pull-up;
+			bias-pull-up-value = "100k";
+			slew-rate = "slow";
+			nxp,speed = "100-mhz";
+		};
+		group1 {
+			pinmux = <&iomuxc_gpio_ad_b1_10_lpuart8_tx>;
+			drive-strength = "r0-6";
+			slew-rate = "slow";
+			nxp,speed = "100-mhz";
+		};
+	};
+
 	pinmux_lpuart3_sleep: pinmux_lpuart3_sleep {
 		group0 {
 			pinmux = <&iomuxc_gpio_ad_b1_06_gpio1_io22>;

boards/nxp/mimxrt1060_evk/mimxrt1060_evk.dtsi

@@ -148,6 +148,13 @@ arduino_i2c: &lpi2c1 {
 	pinctrl-names = "default", "sleep";
 };
 
+&lpuart8 {
+	current-speed = <115200>;
+	pinctrl-0 = <&pinmux_lpuart8>;
+	pinctrl-1 = <&pinmux_lpuart8_sleep>;
+	pinctrl-names = "default", "sleep";
+};
+
 &enet_mac {
 	status = "okay";
 	pinctrl-0 = <&pinmux_enet>;