usb: typec: mux: Add helpers for setting the mux state

Adding helpers typec_switch_set() and typec_mux_set() that
simply call the ->set callback function of the mux. These
functions make it possible to set the mux states also from
outside the class code.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20200302135353.56659-3-heikki.krogerus@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>