Ensures RWDT remains alert throughout the boot process if enabled.

This patch applies the change to the following SoCs: r8a774a1,
r8a774b1 and r8a774c0.
Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
Link: https://lore.kernel.org/r/20200616162626.27944-4-uli+renesas@fpond.euSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>