lxd/instance/drivers/driver/qemu/bus: Adds comments, clarifies var names, and constants for defined multi-function groups
lxd/instance/drivers/driver/qemu/bus: Adds comments, clarifies var names, and constants for defined multi-function groups

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

stgraber/lxd,Skarlso/lxd,atxwebs/lxd,atxwebs/lxd,hallyn/lxd,hallyn/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,mjeanson/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,Skarlso/lxd,lxc/lxd,Skarlso/lxd,Skarlso/lxd,mjeanson/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,mjeanson/lxd