license: cleanup: add SPDX Apache-2.0 license identifier

Update the files which contain no license information with the
'Apache-2.0' SPDX license identifier.  Many source files in the tree are
missing licensing information, which makes it harder for compliance
tools to determine the correct license.

By default all files without license information are under the default
license of Zephyr, which is Apache version 2.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

include/linker/app_smem.ld

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 /*
  * This hackish way of including files is due to CMake issues:
  *   https://gitlab.kitware.com/cmake/cmake/issues/11985

include/linker/app_smem_aligned.ld

@@ -1,2 +1,4 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 /* space holder  */
 APP_SMEM_SECTION()

include/linker/app_smem_unaligned.ld

@@ -1,2 +1,4 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 /* space holder  */
 APP_SMEM_SECTION()

include/linker/common-ram.ld

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 	SECTION_DATA_PROLOGUE(initlevel,,)
 	{
 		DEVICE_INIT_SECTIONS()

include/linker/common-rom.ld

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 #if defined(CONFIG_GEN_ISR_TABLES) && !defined(CONFIG_DYNAMIC_INTERRUPTS)
 	SECTION_PROLOGUE(sw_isr_table,,)
 	{

include/linker/debug-sections.ld

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 	/* following sections are obtained via 'ld --verbose' */
 
 	/* Stabs debugging sections. */

include/linker/kobject-text.ld

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 #ifdef CONFIG_USERSPACE
 	/* We need to reserve room for the gperf generated hash functions.
 	 * Fortunately, unlike the data tables, the size of the code is

include/linker/rel-sections.ld

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 	/*
 	 * .rel.* are for relocation.
 	 * These are being produced by compiler/linker.