drm/i915: Nuke intel_bw_calc_min_cdclk()

drm/i915: Nuke intel_bw_calc_min_cdclk()

intel_bw_calc_min_cdclk() is entirely pointless. All it manages to do is
somehow conflate the per-pipe min cdclk with dbuf min cdclk. There is no
(at least documented) dbuf min cdclk limit on pre-skl so let's just get
rid of all this confusion.

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220303191207.27931-6-ville.syrjala@linux.intel.com