dt-bindings: mux: Document mux-states property

In some cases, it is required to provide the state to which the mux
controller has to be set to, from the consumer device tree node. Document
the property mux-states that can be used for adding this support.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/f4d02ac8-23ee-d891-4056-75c672cc59c9@axentia.se


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