scanpypi: place a warning into *.mk file if licence id couldn't be detected
If a license file could be found, but license id couldn't be detected place
following warning into *.mk file:
FOO_LICENSE = FIXME: license id couldn't be detected
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>