arm64: dts: renesas: r8a77970: sort includes

Sort includes used in r8a77970 DTS to improve maintainability
and for consistency with other R-Car DTS files.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>