drm/i915/ttm: Abort suspend on i915_ttm_backup failure

On system suspend when system memory is low then i915_gem_obj_copy_ttm()
could fail trying to backup a lmem obj. GEM_WARN_ON() is not enough,
suspend shouldn't continue if i915_ttm_backup() throws an error.

v2: Keep the fdo issue till we have a igt test(Matt).
v3: Use %pe(Andrzej)

References: https://gitlab.freedesktop.org/drm/intel/-/issues/6529Reviewed-by: NMatthew Auld <matthew.auld@intel.com>
Reviewed-by: NAndrzej Hajda <andrzej.hajda@intel.com>
Suggested-by: NChris P Wilson <chris.p.wilson@intel.com>
Signed-off-by: NNirmoy Das <nirmoy.das@intel.com>
Signed-off-by: NMatthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220901172217.18392-1-nirmoy.das@intel.com

drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c

@@ -79,7 +79,12 @@ static int i915_ttm_backup(struct i915_gem_apply_to_region *apply,
 		goto out_no_populate;
 
 	err = i915_gem_obj_copy_ttm(backup, obj, pm_apply->allow_gpu, false);
-	GEM_WARN_ON(err);
+	if (err) {
+		drm_err(&i915->drm,
+			"Unable to copy from device to system memory, err:%pe\n",
+			ERR_PTR(err));
+		goto out_no_populate;
+	}
 	ttm_bo_wait_ctx(backup_bo, &ctx);
 
 	obj->ttm.backup = backup;