soc: renesas: Use "#ifdef" for single-symbol definition checks

Replace "#if defined(CONFIG_<foo>)" by "#ifdef CONFIG_<foo>" for
brevity.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/6026a3fe36735f0e6a0ecb037bf7c45f42aa3daf.1678705241.git.geert+renesas@glider.be