device property: Introduce fwnode_find_reference()

In most cases the references that the drivers look for don't
have any arguments. This introduces a wrapper function for
fwnode_property_get_reference_args() that looks for
references by using only the name and index.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>