drm/i915: rename/remove CNL registers

Remove registers that are not used anymore due to CNL removal and rename
those that are.

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/20210728215946.1573015-25-lucas.demarchi@intel.com