ARM: dts: renesas: Add compatible properties to RTL8201FL Ethernet PHYs

Add compatible values to Ethernet PHY subnodes representing Realtek
RTL8201FL PHYs on RZ/A2 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/a23eca16869457684b0300379233e335b4e2047e.1631174218.git.geert+renesas@glider.be