checkpatch: check for SPDX tags of licenses in use

Fix the patch of the external helper spdxcheck.py accordingly to
OpenOCD folder structure.
List only the current LICENSES subfolders in spdxcheck.py .
Enable the check for SPDX headers.
Extend the check for TCL and Makefile.am files.

Change-Id: I0a40da0127746217ee0ac416058d5ceb922428ff
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/5608
Tested-by: jenkins

.checkpatch.conf

@@ -23,7 +23,6 @@
 --ignore PREFER_DEFINED_ATTRIBUTE_MACRO
 --ignore PREFER_FALLTHROUGH
 --ignore PREFER_KERNEL_TYPES
---ignore SPDX_LICENSE_TAG
 --ignore SPLIT_STRING
 --ignore SSCANF_TO_KSTRTO
 --ignore SWITCH_CASE_INDENT_LEVEL