soc: mediatek: pm-domains: Fix the power glitch issue

Power reset maybe generate unexpected signal. In order to avoid
the glitch issue, we need to enable isolation first to guarantee the
stable signal when power reset is triggered.

Fixes: 59b644b0

 ("soc: mediatek: Add MediaTek SCPSYS power domains")
Signed-off-by: Chun-Jie Chen <chun-jie.chen@mediatek.com>
Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Miles Chen <miles.chen@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221014102029.1162-1-allen-kh.cheng@mediatek.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>