dt-bindings: memory: renesas,rpc-if: Document R-Car H3/M3/E3 support

Document support for the SPI Multi I/O Bus Controller (RPC-IF) in the
R-Car H3, M3-W, M3-W+, M3-N, and E3 SoCs.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/3784b6cb76a008fb56d6cb4ba228d78c77e710fa.1648546583.git.geert+renesas@glider.be


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>