drm/i915: Extract intel_cdclk_state

Use the same structure to store the cdclk state in both
intel_atomic_state and dev_priv. First step towards proper
old vs. new cdclk states.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200120174728.21095-10-ville.syrjala@linux.intel.com


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