The new struct will be used in a follow up patch to allow a current and
a staged config to exist for the same shared DPLL.

v2: Rebase on by mask_to_refcount()->hweight32() change. (Damien)
Signed-off-by: NAnder Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>