build: interpose zephyr_flash_debug.py in debug/debugserver targets

Just as was previously done for flashing, invoke zephyr_flash_debug.py
from the build system debug and debugserver targets by default. The
Python script will fall back on the corresponding shell script if it
doesn't have its own implementation.

The shell script can be used instead, just as with flashing, by
setting USE_ZEPHYR_FLASH_DEBUG_SHELL to any nonempty value.

Signed-off-by: Marti Bolivar <marti.bolivar@linaro.org>
2 files changed