drm/i915: Nuke icl_calc_dp_combo_pll_link()

We already have the code to calculate the WRPLL output clock from
the register values, but for some reason we're only using it for
HDMI and not DP. Throw out the inflexible DP DPLL table lookup and
just call the HDMI code which decodes the actual register values.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190207173230.22368-12-ville.syrjala@linux.intel.com
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>