arm64: dts: renesas: r8a779g2: Add White Hawk Single support

arm64: dts: renesas: r8a779g2: Add White Hawk Single support

The White Hawk Single board is a single-board integration of the Renesas
White Hawk CPU and Breakout board stack, based on the R-Car V4H ES2.0
(R8A779G2) SoC.

For now, the only visible differences compared to the board stack are:
  - The SoC is an updated version of R-Car V4H (R8A779G0),
  - The serial console uses an FT2232H instead of a CP2102 USB-UART
    bridge, with CTS/RTS wired.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/2b8d37949c17cca170c1d9e97f10a100b20c5cd9.1706192990.git.geert+renesas@glider.be