software node: Introduce software_node_alloc()/software_node_free()

Introduce software_node_alloc() and software_node_free() helpers.
This will help with code readability and maintenance.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210329151207.36619-2-andriy.shevchenko@linux.intel.com


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