virtio: Fix handling of feature bits >= 32

virtio: Fix handling of feature bits >= 32

Fix handling of feature bits >= 32.  This does not yet affect any driver
as no high feature bit besides VERSION_1 is used, and that one has
special handling.

Also, with VIRTIO_DEBUG, simply walk through all transport and device
feature names, so that we don't need to adjust the if clause whenever
the standard introduces new transport features.

ok jan@ bluhm@