nodedev: Revert auto-start property for mdevs

nodedev: Revert auto-start property for mdevs

We supported autostart of node devices via an xml element, but this
is not consistent with other libvirt objects which use an explicit API
for setting autostart status. So revert this and implement it as an
official API in a future commit.

The initial support was refactored after merging, so this commit reverts
both of those previous commits.

Revert "virNodeDevCapMdevParseXML: Use virXMLPropEnum() for ./start/@type"
This reverts commit 9d4cd1d1cda84aa15b77a506f2ad6362a74edf1a.

Revert "nodedev: support auto-start property for mdevs"
This reverts commit 42a558549935336cbdb7cbfe8b239ffb0e3442e3.

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>