drm/i915/dpt: Evict all DPT VMAs on suspend

drm/i915/dpt: Evict all DPT VMAs on suspend

Currently intel_dpt_resume() tries to blindly rewrite all the
PTEs for currently bound DPT VMAs. That is problematic because
the CPU mapping for the DPT is only really guaranteed to exist
while the DPT object has been pinned. In the past we worked
around this issue by making DPT objects unshrinkable, but that
is undesirable as it'll waste physical RAM.

Let's instead forcefully evict all the DPT VMAs on suspend,
thus guaranteeing that intel_dpt_resume() has nothing to do.
To guarantee that all the DPT VMAs are evictable by
intel_dpt_suspend() we need to flush the cleanup workqueue
after the display output has been shut down.

And for good measure throw in a few extra WARNs to catch
any mistakes.

Cc: Brian Geffon <bgeffon@google.com>
Cc: Vidya Srinivas <vidya.srinivas@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241127061117.25622-4-ville.syrjala@linux.intel.com
Reviewed-by: Vidya Srinivas <vidya.srinivas@intel.com>
Tested-by: Vidya Srinivas <vidya.srinivas@intel.com>