tcl/interface: add SPDX tag

tcl/interface: 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/interface | 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: I7bd6a628e9e153fc477cddf9b97087a39ec48aa7
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7029
Tested-by: jenkins