platform/chrome: cros_ec_typec: Get retimer handle

Where available, obtain the handle to retimer switch specified via
firmware, and update the mux configuration callsites to add retimer
support for supported modes.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220816214857.2088914-8-pmalani@chromium.org