drm/i915: Start tracking voltage level in the cdclk state

drm/i915: Start tracking voltage level in the cdclk state

For CNL we'll need to start considering the port clocks when we select
the voltage level for the system agent. To that end start tracking the
voltage in the cdclk state (since that already has to adjust it).

v2: s/voltage/voltage_level/ (Rodrigo)

Cc: Mika Kahola <[email protected]>
Cc: Manasi Navare <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Signed-off-by: Ville Syrjälä <[email protected]>
Reviewed-by: Rodrigo Vivi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]