soc: renesas: rcar-rst: Add support for RZ/G2N

Add support for RZ/G2N (R8A774B1) to the R-Car RST driver.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Link: https://lore.kernel.org/r/1568881036-4404-5-git-send-email-biju.das@bp.renesas.com


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