soc: renesas: mark OF related data as maybe unused

soc: renesas: mark OF related data as maybe unused

The driver can be compile tested with !CONFIG_OF making certain data
unused.  With W=1:

    drivers/soc/renesas/renesas-soc.c:272:34: error: ‘renesas_socs’ defined but not used [-Werror=unused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230312132650.352796-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>