QEMU added the machine types for the 5.1 release so let's update them.

Other notable changes are 'cpu-throttle-tailslow' migration property,
'zlib' compression for qcow2 images and absrtact socket support.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>