spapr: Clean up spapr_dr_connector_by_*()

spapr: Clean up spapr_dr_connector_by_*()

 * Change names to something less ludicrously verbose
 * Now that we have QOM subclasses for the different DRC types, use a QOM
   typename instead of a PAPR type value parameter

The latter allows removal of the get_type_shift() helper.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Acked-by: Michael Roth <mdroth@linux.vnet.ibm.com>