drm/i915: remove explicit CNL handling from intel_wopcm.c

Consider the new WOPCM size as starting in ICL rather than CNL since the
latter is being removed from the driver.

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/20210728215946.1573015-20-lucas.demarchi@intel.com