drm/i915/cdclk: Extract hsw_ips_min_cdclk()

drm/i915/cdclk: Extract hsw_ips_min_cdclk()

Pull the whole BDW IPS min CDCLK stuff into the IPS code
so that all the details around IPS are contained in once
place.

Note that while
- min_cdclk = DIV_ROUND_UP(min_cdclk * 100, 95);
vs.
+ min_cdclk = max(DIV_ROUND_UP(crtc_state->pixel_rate * 100, 95), min_cdclk)
may look different, they are in fact the same because
min_cdclk==crtc_state->pixel_rate at this point in
intel_crtc_compute_min_cdclk() on BDW.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241029215217.3697-4-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>