spi: Add support for software nodes

Making it possible for the drivers to assign complete
software fwnodes to the devices instead of only the device
properties in those nodes.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20210303152814.35070-2-heikki.krogerus@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>