usb: typec: mux: Add CONFIG guards for functions

There are some drivers that can use the Type C mux API, but don't have
to. Introduce CONFIG guards for the mux functions so that drivers can
include the header file and not run into compilation errors on systems
which don't have CONFIG_TYPEC enabled. When CONFIG_TYPEC is not enabled,
the Type C mux functions will be stub versions of the original calls.

Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Link: https://lore.kernel.org/r/20220615172129.1314056-3-pmalani@chromium.org


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