build: use new function get_firmware_filenames() and throw away some hardcoded filenames
(cherry picked from commit a0f17d98d7f7a87a5bac9c07fa86d47ff93a1fd7)

Signed-off-by: Andi Bräu <ab@andi95.de>
build: first try for better individually showing the generated firmware-files after build 5/5
(cherry picked from commit 2d27ea38c0b930d4dd7265e64d37b93917c13382)

Signed-off-by: Andi Bräu <ab@andi95.de>