net: phy: Add support for the DP83TG720S Ethernet PHY

The DP83TG720S-Q1 device is an IEEE 802.3bp and Open Alliance compliant
automotive Ethernet physical layer transceiver.

This driver was tested with i.MX8MP EQOS (stmmac) on the MAC side and
same TI PHY on other side.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20231212054144.87527-3-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>