usb: typec: altmodes/displayport: Add pin assignment helper

usb: typec: altmodes/displayport: Add pin assignment helper

commit 582836e3cfab4faafbdc93bbec96fce036a08ee1 upstream.

The code to extract a peripheral's currently supported Pin Assignments
is repeated in a couple of locations. Factor it out into a separate
function.

This will also make it easier to add fixes (we only need to update 1
location instead of 2).

Fixes: 29d676ffd363 ("usb: typec: altmodes/displayport: correct pin assignment for UFP receptacles")
Cc: stable@vger.kernel.org
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20230111020546.3384569-1-pmalani@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>