Use the infrastructure added in a previous patch to choose shared DPLLs
and calculate clocks before touching the hardware.

v2: Don't set mode_set hooks since dev_priv is kzalloc()'d (Ville)
Signed-off-by: NAnder Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>