arm64: dts: renesas: r8a779a0: Add GPIO nodes

Add device nodes for the General Purpose Input/Output (GPIO) block on
the Renesas R-Car V3U (r8a779a0) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20210114111117.2214281-1-geert+renesas@glider.be