net: phy: at803x: mention AR8033 as same as AR8031

The AR8033 is the AR8031 without PTP support. All other registers are
the same. Unfortunately, they share the same PHY ID. Therefore, we
cannot distinguish between the one with PTP support and the one without.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>