arm64: dts: renesas: r8a774b1: Add VSP instances

The r8a774b1 has 4 VSP instances.

Based on the work done for r8a77965 SoC.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Link: https://lore.kernel.org/r/1569313375-53428-6-git-send-email-biju.das@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>