dt-bindings: arm: renesas: Document R-Car V4H White Hawk DT bindings

Add device tree binding documentation for the Renesas R-Car V4H
(r8a779g0) SoC and the Renesas White Hawk CPU and BreakOut boards.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20220420084255.375700-2-yoshihiro.shimoda.uh@renesas.com
Link: https://lore.kernel.org/r/20220420084255.375700-3-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>