Ensures RWDT remains alert throughout the boot process if enabled.

This patch applies the change to the following SoCs: r8a77950, r8a77951,
r8a77960, r8a77961, r8a77965, r8a77970, r8a77980, r8a77990 and r8a77995.
Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
Link: https://lore.kernel.org/r/20200616162626.27944-3-uli+renesas@fpond.euSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>