samr21-xpro: Can't use `make debug` anymore

[miri64]

Description

Since #11725 got merged make debug does not work for samr21-xpro anymore. I believe it is due to this check

RIOT/makefiles/boards/sam0.inc.mk

Lines 53 to 55 in b617e40

	ifeq ($(PROGRAMMER),openocd)
	include $(RIOTMAKE)/tools/openocd.inc.mk
	endif

as edbg is used as a programmer, but openocd was used in the past for debugging.

Steps to reproduce the issue

Plug-in a samr21-xpro, and type

BOARD=samr21 make -C examples/hello-world

Expected results

make: Entering directory '/home/mlenders/Repositories/RIOT-OS/RIOT/examples/gnrc_networking'
/home/mlenders/Repositories/RIOT-OS/RIOT/dist/tools/openocd/openocd.sh debug /home/mlenders/Repositories/RIOT-OS/RIOT/examples/gnrc_networking/bin/samr21-xpro/gnrc_networking.elf
### Starting Debugging ###
Open On-Chip Debugger 0.10.0+dev-00910-g4dbcb1e7 (2019-06-17-16:24)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
Reading symbols from /home/mlenders/Repositories/RIOT-OS/RIOT/examples/gnrc_networking/bin/samr21-xpro/gnrc_networking.elf...
Remote debugging using :3333
__set_PRIMASK (priMask=1) at include/vendor/cmsis_gcc.h:414
warning: Source file is more recent than executable.
414	  __ASM volatile ("MSR primask, %0" : : "r" (priMask) : "memory");
(gdb) 

Actual results

make: Entering directory '/home/mlenders/Repositories/RIOT-OS/RIOT/examples/gnrc_networking'
make: Leaving directory '/home/mlenders/Repositories/RIOT-OS/RIOT/examples/gnrc_networking'

Versions

Any commit between b617e40 and current master (cd298b9)