In some chipsets, we need to disable EXT_BUCK_ISO before turning on the
specific power pm-domains (mtcmos), such as ADSP in MT8192 and CAM_VCORE
in MT8188.
Add the MTK_SCPD_EXT_BUCK_ISO flag to control the buck isolation setting
in the mediatek power domain driver.
Fixes: 59b644b01cf4 ("soc: mediatek: Add MediaTek SCPSYS power domains")
Signed-off-by: Allen-KH Cheng <allen-kh.cheng@xxxxxxxxxxxx>