Update and remove obsolete package relations

• Add support for per-package Suggests control field
• misc-nonfree: Move all packages from Recommends to Suggests (Closes: #1137651)
• libertas: Remove firmware-marvell-prestera from Recommends
• Remove remains of the firmware-qcom-media to firmware-qcom-soc transition
• libertas: Remove Replaces/Provides relations to libertas-firmware
• misc-nonfree: Remove Provides relation to firmware-{adi,ralink}