As we're doing throughout the code, being optimistic that platform n + 1
will mostly reuse the same things as platform n allows us to minimize
the enabling work needed.

This time, it's about the number of WM levels.
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>