node_device_driver: Deduplicate mediated devices listing

node_device_driver: Deduplicate mediated devices listing

We have virMdevctlListDefined() to list defined mdevs, and
virMdevctlListActive() to list active mdevs. Both have the same
body except for one boolean argument passed to
nodeDeviceGetMdevctlListCommand(). Join the two functions under
virMdevctlList() name and introduce @defined argument that is
then just passed to the cmd line builder function.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>