mm: compaction: Add automatic compaction mechanism

This adds a simple implementation of a scheduled
compaction mechanism.

The scheduled compaction gets executed compaction_soff_delay_ms
(default 3000ms) after the screen gets turned off unless
the compaction_timeout_ms (default 900000ms) prevents
it because a memory compaction is not required.

The workqueue is freezable to indicate that this
shouldn't be running during suspend.

The parameters of the screen off delay and the forced
timeout are configurable.

Co-authored-by: Alex Naidis <alex.naidis@linux.com>
[@0ctobot: Convert to msm_drm_notifier, adapt for msm-4.19,
and accomodate OnePlus' custom BLANK states]
Co-authored-by: Adam W. Willis <return.of.octobot@gmail.com>