arm64: dts: renesas: white-hawk: Add Ethernet sub-board

Add a DTS file for the R-Car V4H White Hawk RAVB/Ethernet(1000Base-T1)
sub-board (RTP8A779G0ASKB0SE0SA000), and include it from the main
r8a779g0-white-hawk.dts.

For now its contents are limited to the Board ID EEPROM.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/991600919513dd05a9a7d9c170c6924baf14d1a2.1662715538.git.geert+renesas@glider.be