mesa: Update VAO internal state when setting the _DrawVAO.

mesa: Update VAO internal state when setting the _DrawVAO.

Update the VAO internal state on Array._DrawVAO instead of
Array.VAO. Also the VAO internal state update gets triggered now
by a change of Array._DrawVAO instead of the _NEW_ARRAY state flag.
Also no driver looks at any VAO's NewArrays value from within
the Driver.UpdateState callback. So it should be safe to move
this update into the _mesa_set_draw_vao method.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Mathias Fröhlich <Mathias.Froehlich@web.de>