drivers property: When no children in primary, try secondary

Software firmware nodes can provide a child node to its parent.
Since software node can be secondary, we need a mechanism to access
the children. The idea is to list children of the primary node first
and when they are finished, continue with secondary node if available.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20200520102959.34812-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>