docs: formatdomain: document versions for video acceleration
docs: formatdomain: document versions for video acceleration

clarify what version initial support was added, and when libvirt
started supporting it for the qemu driver

https://bugzilla.redhat.com/show_bug.cgi?id=657931

libvirt/libvirt,datto/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,zippy2/libvirt,taget/libvirt,eskultety/libvirt,eskultety/libvirt,andreabolognani/libvirt,datto/libvirt,nertpinx/libvirt,libvirt/libvirt,taget/libvirt,jfehlig/libvirt,jardasgit/libvirt,jardasgit/libvirt,andreabolognani/libvirt,olafhering/libvirt,jfehlig/libvirt,jfehlig/libvirt,nertpinx/libvirt,jardasgit/libvirt,crobinso/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,taget/libvirt,zippy2/libvirt,olafhering/libvirt,crobinso/libvirt,zippy2/libvirt,eskultety/libvirt,andreabolognani/libvirt,datto/libvirt,taget/libvirt,taget/libvirt,VenkatDatta/libvirt,zippy2/libvirt,jardasgit/libvirt,libvirt/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,olafhering/libvirt,crobinso/libvirt,VenkatDatta/libvirt,eskultety/libvirt,jardasgit/libvirt,olafhering/libvirt,fabianfreyer/libvirt,libvirt/libvirt,datto/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,crobinso/libvirt,datto/libvirt,jfehlig/libvirt,eskultety/libvirt,nertpinx/libvirt