treewide: fix SPDX tags on existing files

Explicitly state the license in all source files to comply with SPDX
best practices. In addition, update the copyright notice to the new
format.

Note: Cherry-picked only copyright and license notices.

Co-authored-by:    Luca Burelli <l.burelli@arduino.cc>
Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: pillo79

variants/arduino_nano_33_ble/arduino_nano_33_ble.overlay

@@ -1,3 +1,9 @@
+/*
+ * Copyright (c) Arduino s.r.l. and/or its affiliated companies
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 / {
 	zephyr,user {
 		digital-pin-gpios = <&arduino_nano_header 0 0>,

variants/arduino_nano_33_iot/arduino_nano_33_iot.overlay

@@ -1,3 +1,9 @@
+/*
+ * Copyright (c) Arduino s.r.l. and/or its affiliated companies
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 #include <zephyr/dt-bindings/adc/adc.h>
 
 / {

variants/nrf52840dk_nrf52840/nrf52840dk_nrf52840.overlay

@@ -1,3 +1,9 @@
+/*
+ * Copyright (c) Arduino s.r.l. and/or its affiliated companies
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 / {
 	zephyr,user {
 		digital-pin-gpios = <&arduino_header 6 0>,	/* Digital */

variants/nrf9160dk_nrf9160/nrf9160dk_nrf9160.overlay

@@ -1,3 +1,9 @@
+/*
+ * Copyright (c) Arduino s.r.l. and/or its affiliated companies
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 / {
 	zephyr,user {
 		digital-pin-gpios =