net: ethtool: tsinfo: Enhance tsinfo to support several hwtstamp by net topology

Either the MAC or the PHY can provide hwtstamp, so we should be able to
read the tsinfo for any hwtstamp provider.

Enhance 'get' command to retrieve tsinfo of hwtstamp providers within a
network topology.

Add support for a specific dump command to retrieve all hwtstamp
providers within the network topology, with added functionality for
filtered dump to target a single interface.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>