spi: Remove support for dangling device properties

>From now on only accepting complete software nodes.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20210303152814.35070-5-heikki.krogerus@linux.intel.com


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