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: Applied only cores/arduino/time_macros.h on cherry-pick time.

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

Author: 2 people

cores/arduino/time_macros.h

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