Don't freeze apps in the power exemption allow list.

Set the "should not freeze" flag in oom adjuster if the app
is in the power exemption allow list, as it doesn't make sense
to freeze such kind of apps. There is an existing call to
update the oom adj when the power exemption list changes.

Bug: 237178259
Bug: 231253560
Test: Manual - see b/237178259#comment20
Test: atest CachedAppOptimizerTest
Change-Id: I5fd1e623f60680b34096f0e58a088f72bf1089cb