drm/i915: Document which RING_FAULT bits apply to which platforms

The RING_FAULT bits have change a bit over the years. Document
which platforms use which bits.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250211231941.22769-5-ville.syrjala@linux.intel.com