arm64: dts: renesas: r8a774a1: Add pinctrl device node

This patch adds pinctrl device node for R8A774A1 SoC.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>