drm/i915/pch: Hide PCH device IDs

Only the PCH identification code needs the PCH device IDs, as all the
PCH checks are now based on PCH type. Hide the PCH device IDs inside
intel_pch.c. Remove the unused INTEL_PCH_ID() macro while at it.

Reviewed-by: Nemesa Garg <nemesa.garg@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d1ceb9fc461cf21e1b885a55293f593eba1458ea.1738923308.git.jani.nikula@intel.com


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