usb: typec: mux: Introduce indirection

Rather than directly exposing the implementation's representation of the
typec muxes to the controller/clients, introduce an indirection object.

This enables the introduction of turning this relationship into a
one-to-many in the following patch.

Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220422222351.1297276-5-bjorn.andersson@linaro.org


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