usb: typec: tcpm: PD3.0 sinks can send Discover Identity even in device mode

usb: typec: tcpm: PD3.0 sinks can send Discover Identity even in device mode

>From 6.4.4.2 Structured VDM:
• Either Port May be an Initiator of Structured VDMs except for the Enter
Mode and Exit Mode Commands which Shall only be initiated by the DFP."

The above implies that when PD3.0 link is established PD3.0 sinks
can send out discover identity command/AMS once PD negotiation is done.
This allows discovering identity for PD3.0 UFP ports as well.

Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Link: https://lore.kernel.org/r/20210318065604.3757307-1-badhri@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>