drm/mgag200: Invalidate page tables when pinning a BO

drm/mgag200: Invalidate page tables when pinning a BO

When a BO gets pinned the placement may get changed. If the memory is
mapped into user space and user space has already accessed the mapped
range the page tables are set up but now point to the wrong memory.
Set bo.mdev->dev_mapping in mgag200_bo_create() to make sure that
ttm_bo_unmap_virtual() called from ttm_bo_handle_move_mem() will take
care of this.

v2: Don't call ttm_bo_unmap_virtual() in mgag200_bo_pin(), fix comment.

Signed-off-by: Egbert Eich <eich@suse.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>