CVE-2026-72008: 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 HWVOTER type power domains, this driver was unconditionally trying to perform cleanup for DIRECTCTL domains, but only after checking if the target domain is powered on... with the DIRECTCTL scpsysdomainison() code again.

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

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 pmgenpdremove() right before calling poweroff, be cautious and add a variation of the power off functions (with a internal suffix) for those to get a pointer to scpsysdomain instead of one to genericpmdomain as, even if that's still working, this is way too much fragile and would break at some point.