package_manager.py: fixes for multilib deb packaging builds
* tmp/deploy/deb subdirectories do not get hyphens replaced
with underscores, so don't do that translation when building
the sources list.
* Fix MULTILIB_VARIANTS handling to be more general and
work for all architectures
* Also include a fix for a warning generated by apt
due to missing apt/preferences.d directory.
Signed-off-by: Matt Madison <matt@madison.systems> Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
