net: phy: mscc: Add PTP support for 2 more VSC PHYs

Add VSC8572 and VSC8574 in the PTP configuration
as they also support PTP.

The relevant datasheets can be found here:
  - VSC8572: https://www.microchip.com/wwwproducts/en/VSC8572
  - VSC8574: https://www.microchip.com/wwwproducts/en/VSC8574



Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Link: https://lore.kernel.org/r/20201112092250.914079-1-steen.hegelund@microchip.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>