drm/i915: Simplify intel_set_cdclk_{pre,post}_plane_update() calling convention

Move all the old vs. new state shenanigans
into intel_set_cdclk_{pre,post}_plane_update() so that the caller
doesn't need to know any of it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200120174728.21095-9-ville.syrjala@linux.intel.com


Reviewed-by: José Roberto de Souza <jose.souza@intel.com>