drm/i915: Kill PCH_KBP

For us KBP is 100% identical to SPT. Kill the redundant enum
value. Also bspec doesn't talk about KBP either, so this might
avoid some confusion when cross checking the code against the
spec.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190506152627.20283-1-ville.syrjala@linux.intel.com


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