clk: renesas: r9a08g045: Add power domain for RTC

The RTC and VBATTB don't share the MSTOP control bit (but only the bus
clock and the reset signal). As the MSTOP control is modeled though power
domains add power domain support for the RTC device available on the
Renesas RZ/G3S SoC.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20241019084738.3370489-3-claudiu.beznea.uj@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>