make: allow to override RESET and RESET_FLAGS for all boards and tools

[smlng]

Contribution description

This PR adapts Makefiles to allow for overriding the RESET command (or tool) and required RESET_FLAGS (if any present). For some boards like sam0 based once this is already possible, this PR adds this for all remaining.

This is required to allow for custom or special reset commands, for instance when running hardware-in-the-loop tests in a well known (special) environment which might allow to reset a board by controlling the power via a side-channel.

Testing procedure

try to run make reset for you favourite board that should still work. You may also try to run RESET="" RESET_FLAGS="" make reset which than should fail to reset the board.

Issues/PRs references

[MrKevinWeiss]

heh piling up those commits 😆

[smlng]

heh piling up those commits 😆

that's (really) just so we can identify and revert if a certain board or tool fails 😬

[cladmi]

Would be good to verify all the values are still the same with info-debug-variable-RESET and info-debug-variable-RESET_FLAGS for the different configurations and boards.

[cladmi]

If you want to prevent the pattern to be re-appearing in the future, you can add a detection for it in https://github.com/cladmi/RIOT/blob/master/dist/tools/buildsystem_sanity_check/check.sh

I checked the output right now.

#! /bin/sh
BOARDS=$(find boards/* -maxdepth 0 -type d \! -name "common" -exec basename {} \;)

list_all_variables() {
    for BOARD in ${BOARDS}
    do
        export BOARD
        echo ${BOARD}
        make --no-print-directory -C examples/hello-world/ info-debug-variable-RESET info-debug-variable-RESET_FLAGS
    done
}

list_all_variables | tee $1_output_simple
PROGRAMMER=jlink list_all_variables | tee $1_output_jlink

And the output of RESET and RESET_FLAGS is the same also with PROGRAMMER=jlink.

The uniflash 3 looks good even if not re-tested locally.

[cladmi]

Agreed and tested that it did not change the output of RESET and RESET_FLAGS in the default and jlink case.

[cladmi]

It is also a task I would like to have with FLASHER and FFLAGS in general, but the review will be a bit trickier I think.

[smlng]

thanks @cladmi for review and merge!!