drm/i915: Covert remaining platforms to choose DPLLS before disabling CRTCs

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: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>