pmdomain: mediatek: Use OF-specific regulator API to get power domain supply

pmdomain: mediatek: Use OF-specific regulator API to get power domain supply

The MediaTek power domain driver contains a hack that assigns the device
node of the power domain to the struct device of the power domain
controller in order to use the devres regulator API.

Now that there is a proper OF-specific regulator API, and even a devres
version, replace the hack with proper code.

This change is incompatible with incomplete device trees. Instead of
assigning the dummy regulator in cases where the power domain requires
a supply but the device tree does not provide one, the driver will just
error out. This will be seen on the MT8390 EVK, which is missing
supplies for the IMG_VCORE and CAM_VCORE domains. And likely all the
MediaTek EVBs, which have no power domain supplies specified. This is
however the correct behavior. If the power domain's supply is missing,
then it should not work. Relying on other parts of the system to keep
the unattached regulator enabled is likely to break in ways less easier
to understand.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20240930044525.2043884-4-wenst@chromium.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>