qom: Move HMP command handlers to qom/

qom: Move HMP command handlers to qom/

Move the HMP command handlers related to QOM handlers from
monitor/hmp-cmds.c and qdev-monitor.c to new qom/qom-hmp-cmds.c, where
they are covered by MAINTAINERS section QOM.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Daniel P. Berrange" <berrange@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190619201050.19040-7-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
[Also move hmp_info_qom_tree(), tweak commit message accordingly]