ARM: dts: renesas: Add compatible properties to KSZ8041 Ethernet PHYs

Add compatible values to Ethernet PHY subnodes representing Micrel
KSZ8041 PHYs on RZ/G1 and R-Car Gen2 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/f9e26625924f90eff34fe6f6f02b15fa272c5d80.1631174218.git.geert+renesas@glider.be