memory: renesas-rpc-if: Add support for R-Car Gen4

The SPI Multi I/O Bus Controller (RPC-IF) on R-Car Gen4 SoCs is very
similar to the RPC-IF on R-Car Gen3 SoCs.  It does support four instead
of three bits of strobe timing adjustment (STRTIM), and thus requires a
new mask and new settings.

Inspired by a patch in the BSP by Cong Dang.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/4d0824bf5ed0fb95c51cd36f9a3f0f562b1a6bf8.1665583089.git.geert+renesas@glider.be


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