ARM: dts: renesas: Add compatible properties to uPD6061x Ethernet PHYs

Add compatible values to Ethernet PHY subnodes representing Renesas
uPD60610 or uPD60611 PHYs on RZ/A1 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>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/335a1dfea905369da683e122e41e08ca1c5f90f7.1631174218.git.geert+renesas@glider.be