drm/ttm: remove ttm_bo_wait_unreserved

With nouveau fixed all ttm-using drives have the correct nesting of
mmap_sem vs dma_resv, and we can just lock the buffer.

Assuming I didn't screw up anything with my audit of course.

v2:
- Dont forget wu_mutex (Christian König)
- Keep the mmap_sem-less wait optimization (Thomas)
- Use _lock_interruptible to be good citizens (Thomas)

v3: Rebase over fault handler helperification.

Reviewed-by: Christian König <christian.koenig@amd.com> (v2)
Reviewed-by: Thomas Hellström <thellstrom@vmware.com> (v2)
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: "VMware Graphics" <linux-graphics-maintainer@vmware.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191104173801.2972-3-daniel.vetter@ffwll.ch

include/drm/ttm/ttm_bo_api.h

@@ -154,7 +154,6 @@ struct ttm_tt;
  * @offset: The current GPU offset, which can have different meanings
  * depending on the memory type. For SYSTEM type memory, it should be 0.
  * @cur_placement: Hint of current placement.
- * @wu_mutex: Wait unreserved mutex.
  *
  * Base class for TTM buffer object, that deals with data placement and CPU
  * mappings. GPU mappings are really up to the driver, but for simpler GPUs
@@ -222,8 +221,6 @@ struct ttm_buffer_object {
 	uint64_t offset; /* GPU address space is independent of CPU word size */
 
 	struct sg_table *sg;
-
-	struct mutex wu_mutex;
 };
 
 /**
@@ -707,7 +704,6 @@ ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
 int ttm_bo_swapout(struct ttm_bo_global *glob,
 			struct ttm_operation_ctx *ctx);
 void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
-int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo);
 
 /**
  * ttm_bo_uses_embedded_gem_object - check if the given bo uses the