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

The SPI driver for 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/20210102115412.3402059-3-aford173@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>