usb: typec: Hide the port_type attribute when it's not supported

usb: typec: Hide the port_type attribute when it's not supported

The port_type attribute is special. It is meant to allow
changing the capability of the port in runtime. It is purely
Linux kernel specific feature, i.e. the feature is not
described in any of the USB specifications.

Because of the special nature of this attribute, handling it
differently compared to the other writable attributes, and
hiding it when the underlying port interface (or just the
driver) does not support the feature.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20200211112531.86510-3-heikki.krogerus@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>