pmdomain: mediatek: Fix possible nullptr KP in HWV cleanup/on-check

In the Linux kernel, the following vulnerability has been resolved:

pmdomain: mediatek: Fix possible nullptr KP in HWV cleanup/on-check

Should probe fail for HW_VOTER type power domains, this driver was
unconditionally trying to perform cleanup for DIRECT_CTL domains,
but only after checking if the target domain is powered on... with
the DIRECT_CTL scpsys_domain_is_on() code again.

And there's more: the scpsys_domain_is_on() function is also being
unconditionally used in the probe path, for any power domain that
has flag MTK_SCPD_KEEP_DEFAULT_OFF!

This bug was never experienced by anyone because the HWV domains
never failed probe, and because none of those is declared with the
aforementioned flag - but it's still something critical.

In order to fix this, add a check for MTCMOS Type and, based on
that, call the correct functions for an "is on" check, and also
do the same for the cleanup path, calling the correct functions
for the "power off" action.

For the latter, since there's a call to pm_genpd_remove() right
before calling power_off, be cautious and add a variation of the
power off functions (with a _internal suffix) for those to get a
pointer to scpsys_domain instead of one to generic_pm_domain as,
even if that's still working, this is way too much fragile and
would break at some point.