device property: Add fwnode_get_named_child_node()

Since now we have means to enumerate all children of any fwnode even in
ACPI we can implement fwnode_get_named_child_node(). This is similar than
device_get_named_child_node() with the exception that it can be called to
any fwnode handle. Make device_get_named_child_node() call directly this
new function.

This is useful in cases where we need to be able to find child nodes which
are not direct descendants of the parent device.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>