arm64: dts: renesas: Add compatible properties to RTL8211E Ethernet PHYs

Add compatible values to Ethernet PHY subnodes representing Realtek
RTL8211E PHYs on RZ/G2 boards.  This allows software to identify the PHY
model at any time, regardless of the state of the PHY reset line.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/3b366e3dddd4d3cd7e89b92d3a8f78f6dc18e244.1631174218.git.geert+renesas@glider.be