UBUNTU: [Packaging] final-checks: Depend on makefile flavours

UBUNTU: [Packaging] final-checks: Depend on makefile flavours

The available ABI files do not depend on the config flavours but
those actually built. So instead of looking at the config files,
parse the flavours variable of the <arch>.mk files.

This handles the case where we would like to drop certain flavours
or even whole architectures in backport kernels. Removing the
configuration file is bad because that would cause a huge delta
everytime we rebase (a local mangle would to remove the config
file each time and then the next updateconfigs would re-arrange
things based on that).

Instead we can rely on the information in the architecture
specific rules.

Ignore: yes
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>