boards/nxp: mcxn: Enable LPUART pin internal pullup resistor

This commit enables MCXN236, MCXN947 LPUART pin internal
pullup resistor. For MCXN947 and MCXN236, during LPUAR
initialization, the RX pin is pulled down internally
and STAT [RAF] is set to one. In this state, attempting
to enter low power mode will trigger LPACK reset and
therefore cannot truly enter low power mode. The correct
setting should be to enable LPUART pin internal pullup resistor.

Signed-off-by: Zhaoxiang Jin <Zhaoxiang.Jin_1@nxp.com>

Author: ZhaoxiangJin

boards/nxp/frdm_mcxn236/frdm_mcxn236-pinctrl.dtsi

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 NXP
+ * Copyright 2024-2025 NXP
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -14,6 +14,7 @@
 			slew-rate = "fast";
 			drive-strength = "low";
 			input-enable;
+			bias-pull-up;
 		};
 	};
 
@@ -48,6 +49,7 @@
 			slew-rate = "fast";
 			drive-strength = "low";
 			input-enable;
+			bias-pull-up;
 		};
 	};
 

boards/nxp/frdm_mcxn947/frdm_mcxn947-pinctrl.dtsi

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 NXP
+ * Copyright 2024-2025 NXP
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -62,6 +62,7 @@
 			slew-rate = "fast";
 			drive-strength = "low";
 			input-enable;
+			bias-pull-up;
 		};
 	};
 
@@ -72,6 +73,7 @@
 			slew-rate = "fast";
 			drive-strength = "low";
 			input-enable;
+			bias-pull-up;
 		};
 	};