samples: boards: nrf: system_off: fix includes

Include only what is needed, also sort includes properly.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

samples/boards/nrf/system_off/src/main.c

@@ -4,15 +4,19 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include "retained.h"
+
+#include <inttypes.h>
 #include <stdio.h>
 
-#include <zephyr/kernel.h>
 #include <zephyr/device.h>
+#include <zephyr/kernel.h>
 #include <zephyr/pm/device.h>
 #include <zephyr/sys/poweroff.h>
-#include <soc.h>
-#include "retained.h"
+#include <zephyr/sys/util.h>
+
 #include <hal/nrf_gpio.h>
+#include <soc.h>
 
 #define BUSY_WAIT_S 2U
 #define SLEEP_S 2U

samples/boards/nrf/system_off/src/retained.c

@@ -4,13 +4,17 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include "retained.h"
+
+#include <stdint.h>
 #include <string.h>
+
 #include <zephyr/kernel.h>
 #include <zephyr/devicetree.h>
 #include <zephyr/sys/byteorder.h>
 #include <zephyr/sys/crc.h>
+
 #include <hal/nrf_power.h>
-#include "retained.h"
 
 /* nRF52 RAM (really, RAM AHB slaves) are partitioned as:
  * * Up to 8 blocks of two 4 KiBy byte "small" sections

samples/boards/nrf/system_off/src/retained.h

@@ -7,7 +7,8 @@
 #ifndef RETAINED_H_
 #define RETAINED_H_
 
-#include <inttypes.h>
+#include <stdbool.h>
+#include <stdint.h>
 
 /* Example of validatable retained data. */
 struct retained_data {