drm/i915/cdclk: Extract intel_audio_min_cdclk()

drm/i915/cdclk: Extract intel_audio_min_cdclk()

Pull the audio min cdclk calculation into a helper and hide
it inside intel_audio.c in order to keep most audio related
details in one place.

The one audio related thing that remains in intel_cdclk.c
is commit 451eaa1a614c ("drm/i915: Bump GLK CDCLK frequency when
driving multiple pipes") but given that's implemented in terms
of the cdclk_state I think it should stay put.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241029215217.3697-5-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>