virtio: add interrupt declarations

Change-Id: Ifd68f69599a8313615c31b85828aa5b96c68c165
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4069
Reviewed-by: X512 <danger_mail@list.ru>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

add VirtIO header

Change-Id: I938e80fe156a0a1d49e0eef330cbfc0cf22f0995
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4002
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>