device property: Fallback to secondary fwnode if primary misses the property

The struct fwnode has notion of secondary fwnode. This is supposed to used
as fallback if the primary firmware interface (DT, ACPI) does not have the
property in question.

However, the current implementation never checks the secondary node which
prevents one to add default "built-in" properties to devices.

This patch adds fallback to the secondary fwnode if the primary fwnode
returns that the property does not exists.

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