Made sgabios multiarch aware by adding 'Multi-Arch: foreign' to d/control

Reported by mjt at http://bugs.debian.org/731490 - Thanks!
Updated Standards-Version to 3.9.5 (from 3.9.4)

No changes to the packaging were needed for that - at least according to the
unofficial "Policy checklist for upgrading your packages" found at:
http://www.debian.org/doc/packaging-manuals/upgrading-checklist.txt