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

The only real platform with DISPLAY_VER == 10 is GLK. We don't need to
handle CNL explicitly in intel_ddi.c.

A lot of special code for CNL can be removed. There were some
__cnl.*() functions that were created to share the implementation
between ICL and CNL. Those are now embedded in the only caller, in ICL.

Remove code and rename functions/macros accordingly to use ICL prefix
for those that are still needed.

Verified with:

	make EXTRA_CFLAGS=-Wunused drivers/gpu/drm/i915/display/intel_dpll_mgr.o

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210729233934.2059489-1-lucas.demarchi@intel.com