drm/vmwgfx: Allow the UPDATE_LAYOUT ioctl from control nodes

On vmware there is a daemon telling the KMS system about the GUI layout.
Typically it talks to the X server but in the absence of an X server or if
there are multiple, it wants to talk directly to the vmwgfx kernel module.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>