drm/i915: Use ELK stolen memory reserved detection for ILK

drm/i915: Use ELK stolen memory reserved detection for ILK

While I have no solid proof that ILK follows the ELK path when it
comes to the stolen memory reserved area, there are some hints that
it might be the case. Unfortunately my ILK doesn't have this enabled,
and no way to enable it via the BIOS it seems.

So let's have ILK use the ELK code path, and let's toss in a WARN
into the code to see if we catch anyone with an ILK that has this
enabled to further analyze the situation.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171102151737.23336-3-ville.syrjala@linux.intel.com
Acked-by: Paulo Zanoni <paulo.r.zanoni@intel.com>