ASoC: simple-card: Handle additional devices

An additional-devs subnode can be present in the simple-card top node.
This subnode is used to declared some "virtual" additional devices.

Create related devices from this subnode and avoid this subnode presence
to interfere with the already supported subnodes analysis.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20230623085830.749991-14-herve.codina@bootlin.com


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