drm/ttm: ttm_bo_swapout_all doesn't use it's argument.

Just drop the argument from this.

This does ask the question if this is the function vmwgfx
should be using or should it be doing an evict all like
the other drivers.

Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200728034254.20114-1-airlied@gmail.com