usb: typec: tcpm: Respond Not_Supported if no snk_vdo

If snk_vdo is not populated from fwnode, it implies the port does not
support responding to SVDM commands. Not_Supported Message shall be sent
if the contract is in PD3. And for PD2, the port shall ignore the
commands.

Fixes: 193a6801

 ("staging: typec: tcpm: Respond to Discover Identity commands")
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Kyle Tso <kyletso@google.com>
Link: https://lore.kernel.org/r/20210523015855.1785484-3-kyletso@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>