Documentation: typec.rst: Use literal-block element with ascii art

Using reStructuredText literal-block element with ascii-art.
That prevents the ascii art from being processed as
reStructuredText.

Reported-by: Masanari Iida <standby24x7@gmail.com>
Reviewed-and-tested-by: Jani Nikula <jani.nikula@intel.com>
Fixes: bdecb33a ("usb: typec: API for controlling USB Type-C Multiplexers")
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>