tcl/board: add SPDX tag

For historical reasons, no license information was added to the
tcl files. This makes trivial adding the SPDX tag through script:
	fgrep -rL SPDX tcl/board | while read a;do \
	sed -i '1{i# SPDX-License-Identifier: GPL-2.0-or-later\n
	}' $a;done

With no specific license information from the author, let's extend
the OpenOCD project license GPL-2.0-or-later to the files.

Change-Id: Ibcf7da62e842aafd036a78db9ea2b9f11f79af16
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7028
Tested-by: jenkins
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>