ARM: dts: renesas: Add Renesas Gray Hawk boards support

Initial support for the Renesas Gray Hawk CPU and BreakOut boards.

The arch/arm/dts/r8a779h0-gray-hawk-cpu.dtsi is extended version of:
https://lore.kernel.org/linux-renesas-soc/b657402113267acd57aece0b4c681b707e704455.1706194617.git.geert+renesas@glider.be/


The version currenty submitted upstream lacks functionality which is
present in this series. Once the upstream support implements that
missing functionality, these DTs will be updated to match.

Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>