drm/xe: evict user memory in PM notifier

In the case of VRAM we might need to allocate large amounts of
GFP_KERNEL memory on suspend, however doing that directly in the driver
.suspend()/.prepare() callback is not advisable (no swap for example).

To improve on this we can instead hook up to the PM notifier framework
which is invoked at an earlier stage. We effectively call the evict
routine twice, where the notifier will have hopefully have cleared out
most if not everything by the time we call it a second time when
entering the .suspend() callback. For s4 we also get the added benefit
of allocating the system pages before the hibernation image size is
calculated, which looks more sensible.

Note that the .suspend() hook is still responsible for dealing with all
the pinned memory. Improving that is left to another patch.

Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1181
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4288
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4566
Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://lore.kernel.org/r/20250416150913.434369-6-matthew.auld@intel.com

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