drm/i915/cdclk: abstract intel_cdclk_actual() and intel_cdclk_actual_voltage_level()

Add intel_cdclk_actual() and intel_cdclk_actual_voltage_level() helpers
to avoid looking at struct intel_cdclk_state internals outside of
intel_cdclk.c.

v2: Better location (Imre)

Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/241a9b80a8262b82fded54707ca5622af215dd86.1750847509.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>