ASoC: dt-bindings: simple-mux: add idle-state property

ASoC: dt-bindings: simple-mux: add idle-state property

simple-mux immediately activates the new output, even when it is powered
down. This can be undesirable in some cases, for example when a
mechanical relais is used.
Adds "idle-state" property from the mux controller to select the output
state to be used when the mux is powered down.

Signed-off-by: Hendrik v. Raven <h.v.raven@merzmedtech.de>
Link: https://patch.msgid.link/20241114-simple-mux-idle-state-v2-2-a30cb37d2be2@merzmedtech.de
Signed-off-by: Mark Brown <broonie@kernel.org>