DroneCAN: added FlexDebug support #40790

Job	Run time
build (base)	8m 46s
build (clang)	4m 25s
build-gcc-heli	4m 8s
autotest-heli (sitltest-heli)	10m 1s
autotest (sitltest-copter-tests1a)	7m 14s
autotest (sitltest-copter-tests1b)	9m 33s
autotest (sitltest-copter-tests1c)	11m 23s
autotest (sitltest-copter-tests1d)	8m 45s
autotest (sitltest-copter-tests1e)	8m 51s
autotest (sitltest-copter-tests2a)	8m 55s
autotest (sitltest-copter-tests2b)	28m 36s
	1h 50m 37s

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