drm/i915/display/dg2: Set CD clock squashing registers

Set CD clock squashing registers based on selected CD clock.

v2: use slk_cdclk_decimal() to compute decimal values instead of a
    specific table (Ville)
    Set waveform based on CD clock table (Ville)
    Drop unnecessary local variable (Ville)
v3: Correct function naming (Ville)
    Correct if-else structure (Ville)
[v4: vsyrjala: Fix spaces vs. tabs]
[v5: vsyrjala: Fix cd2x divider calculation (Uma),
               Add warn to waveform lookup (Uma),
               Handle bypass freq in waveform lookup,
               Generalize waveform handling in bxt_set_cdclk()]

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211119131348.725220-4-mika.kahola@intel.com