drm/i915: Catch non-existent registers in find_fw_domain

Add WARN_ON to find_fw_domain to registers related to uninitialized
hardware.

v2:
- Print the uninitialized domains and register (Chris)

Cc: Imre Deak <imre.deak@intel.com>
Cc: Wang Elaine <elaine.wang@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1481120559-17413-1-git-send-email-joonas.lahtinen@linux.intel.com

drivers/gpu/drm/i915/intel_uncore.c

@@ -625,7 +625,14 @@ find_fw_domain(struct drm_i915_private *dev_priv, u32 offset)
 			dev_priv->uncore.fw_domains_table_entries,
 			fw_range_cmp);
 
-	return entry ? entry->domains : 0;
+	if (!entry)
+		return 0;
+
+	WARN(entry->domains & ~dev_priv->uncore.fw_domains,
+	     "Uninitialized forcewake domain(s) 0x%x accessed at 0x%x\n",
+	     entry->domains & ~dev_priv->uncore.fw_domains, offset);
+
+	return entry->domains;
 }
 
 static void