drm/i915: Re-order if/else ladder in intel_detect_pch()

Follow the convention of checking the last platform first and reword the
comment to convey there are more platforms than just DG1.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230919192128.2045154-5-lucas.demarchi@intel.com