drm/i915/display: remove explicit CNL handling from intel_combo_phy.c

The only real platform with DISPLAY_VER == 10 is GLK, that doesn't have
combo phys. We don't need to handle CNL explicitly in
intel_combo_phy.c.

Remove code and rename functions/macros accordingly to use ICL prefix.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210728215946.1573015-5-lucas.demarchi@intel.com