memory: renesas-rpc-if: Add RZ/G2 to Kconfig description

The Renesas RPC-IF is present on the RZ/G2 Series.  Add that to
the description.

Suggested-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210102115412.3402059-2-aford173@gmail.com


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>