drm/i915: Use short PCH names consistently

The comments regarding PCH compatibility use long vs.
short names inconsistently. Just use short names always.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220630150600.24611-2-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>