make/usb_board_reset: define {preflash,term}-delay when necessary

[aabadie]

Contribution description

When running make info-boards-supported in an application directory, I got several warning from make:

$ make -C examples/hello-world info-boards-supported --no-print-directory 
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:32: warning: overriding recipe for target 'preflash-delay'
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:32: warning: ignoring old recipe for target 'preflash-delay'
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:35: warning: overriding recipe for target 'term-delay'
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:35: warning: ignoring old recipe for target 'term-delay'
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:32: warning: overriding recipe for target 'preflash-delay'
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:32: warning: ignoring old recipe for target 'preflash-delay'
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:35: warning: overriding recipe for target 'term-delay'
/work/riot/RIOT/makefiles/tools/usb_board_reset.mk:35: warning: ignoring old recipe for target 'term-delay'
...

The warnings are also printed with the generate-Makefile.ci target.

It seems the usb_board_reset.mk is included several times which leads to the warning. The idea of this PR is to only define preflash-delay and term_delay when necessary, e.g when a related target is used (flash, flash-only => preflash-delay, term => term-delay).

Testing procedure

• Green CI
• Affected boards work the same. I tested it with adafruit-clue and boards/adafruit-clue: use shared usb_board_reset.mk for flash/reset/term targets #19616 and it works as expected, the right delays are applied
• Most important: warnings are gone :)

Issues/PRs references

This is the reason for #19616, I needed a board that is using a {preflash,term}-delay defined in usb_board_reset.mk.

[riot-ci]

Murdock results

✔️ PASSED

f25731e make/usb_board_reset: define {preflash,term}-delay when necessary

Success	Failures	Total	Runtime
6930	0	6931	10m:25s

Artifacts

• Documentation preview

[aabadie]

bors merge

[bors]

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• Murdock
• static-tests
• tools-build-success