This commit overrides the default flash recipe with an edbg specific
one.
The new recipe first verifies the flashfile agains the device flash. If
it is already on there, it won't get overridden.
edbg takes care of resetting the device in any case.
Handle that `IMAGE_OFFSET` can be set to something that contain spaces.
With 'IMAGE_OFFSET=$$((0x1000 + 0x1000))' we had in the command line when doing
'flash'
--offset $((0x1000 --offset + --offset 0x1000))
With the change we correctly have
--offset $((0x1000 + 0x1000))
Allow flashing with an offset in ROM from the rom base address.
It reuses `IMAGE_OFFSET` configuration variable name from `openocd.sh`.
This will allow flashing multiple images with different flash operations.
