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>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -300,6 +300,12 @@ static void g4x_get_stolen_reserved(struct drm_i915_private *dev_priv,
 		return;
 	}
 
+	/*
+	 * Whether ILK really reuses the ELK register for this is unclear.
+	 * Let's see if we catch anyone with this supposedly enabled on ILK.
+	 */
+	WARN(IS_GEN5(dev_priv), "ILK stolen reserved found? 0x%08x\n", reg_val);
+
 	*base = (reg_val & G4X_STOLEN_RESERVED_ADDR2_MASK) << 16;
 
 	WARN_ON((reg_val & G4X_STOLEN_RESERVED_ADDR1_MASK) < *base);
@@ -466,14 +472,12 @@ int i915_gem_init_stolen(struct drm_i915_private *dev_priv)
 	case 3:
 		break;
 	case 4:
-		if (IS_G4X(dev_priv))
-			g4x_get_stolen_reserved(dev_priv,
-						&reserved_base, &reserved_size);
-		break;
+		if (!IS_G4X(dev_priv))
+			break;
+		/* fall through */
 	case 5:
-		/* Assume the gen6 maximum for the older platforms. */
-		reserved_size = 1024 * 1024;
-		reserved_base = stolen_top - reserved_size;
+		g4x_get_stolen_reserved(dev_priv,
+					&reserved_base, &reserved_size);
 		break;
 	case 6:
 		gen6_get_stolen_reserved(dev_priv,