Draft: d/b/gencontrol.py: Build image meta-packages from signed linux-image packages

With af3f1174 ("Introduce a base package for version sync") we lost that the linux-image meta-packages are only available once the signed linux-image packages are available, causing a temporary uninstallability situation.

Move the generation of the linux image meta packages back to the signed linux-image source packages.

Fixes: af3f1174 ("Introduce a base package for version sync") Closes: #1124667 Signed-off-by: Salvatore Bonaccorso carnil@debian.org