dt-bindings: reset: rcar-rst: Document r8a774c0 rst

Document bindings for the RZ/G2E (a.k.a. R8A774C0) reset
module.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>