drm/nouveau: Revert "bus: remove cpu_coherent flag"

This reverts commit aff51175.

The commit caused fence timeouts within nvc0_screen_destroy and most likely
other places as well.

The most obvious effect is, that userspace processes take minutes to
actually quit.
Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/include/nvkm/core/device.h

@@ -175,6 +175,7 @@ struct nvkm_device_func {
 	void (*fini)(struct nvkm_device *, bool suspend);
 	resource_size_t (*resource_addr)(struct nvkm_device *, unsigned bar);
 	resource_size_t (*resource_size)(struct nvkm_device *, unsigned bar);
+	bool cpu_coherent;
 };
 
 struct nvkm_device_quirk {

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -209,7 +209,8 @@ nouveau_bo_new(struct drm_device *dev, int size, int align,
 	nvbo->tile_flags = tile_flags;
 	nvbo->bo.bdev = &drm->ttm.bdev;
 
-	nvbo->force_coherent = flags & TTM_PL_FLAG_UNCACHED;
+	if (!nvxx_device(&drm->device)->func->cpu_coherent)
+		nvbo->force_coherent = flags & TTM_PL_FLAG_UNCACHED;
 
 	nvbo->page_shift = 12;
 	if (drm->client.vm) {

drivers/gpu/drm/nouveau/nvkm/engine/device/pci.c

@@ -1614,6 +1614,7 @@ nvkm_device_pci_func = {
 	.fini = nvkm_device_pci_fini,
 	.resource_addr = nvkm_device_pci_resource_addr,
 	.resource_size = nvkm_device_pci_resource_size,
+	.cpu_coherent = !IS_ENABLED(CONFIG_ARM),
 };
 
 int

drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c

@@ -245,6 +245,7 @@ nvkm_device_tegra_func = {
 	.fini = nvkm_device_tegra_fini,
 	.resource_addr = nvkm_device_tegra_resource_addr,
 	.resource_size = nvkm_device_tegra_resource_size,
+	.cpu_coherent = false,
 };
 
 int