docs: Document the new hostdev type 'mdev'
docs: Document the new hostdev type 'mdev'

Signed-off-by: Erik Skultety <2c14d38fa47c8799f1b9c16280abe27f8edfec6e@redhat.com>

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