arm64: dts: renesas: r8a779a0: Update to R-Car Gen4 compatible values

Despite the name, R-Car V3U is the first member of the R-Car Gen4
family.  Hence update the compatible properties in various device nodes
to include family-specific compatible values for R-Car Gen4:
  - GPIO.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/b477eea0fc33a055d1b1874847e26614f68f5da0.1654701299.git.geert+renesas@glider.be