drm/i915: redefine WARN_ON_ONCE to include the condition

Same as

commit c883ef1b
Author: Mika Kuoppala <miku@iki.fi>
Date:   Tue Oct 28 17:32:30 2014 +0200

    drm/i915: Redefine WARN_ON to include the condition

but for WARN_ON_ONCE. Since the kernel WARN_ON_ONCE actually picks up
*our* version of WARN_ON, we end up with messages like

[  838.285319] WARN_ON(!__warned)

which are not that helpful.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -70,6 +70,9 @@
 #define WARN_ON(x) WARN((x), "WARN_ON(" #x ")")
 #endif
 
+#undef WARN_ON_ONCE
+#define WARN_ON_ONCE(x) WARN_ONCE((x), "WARN_ON_ONCE(" #x ")")
+
 #define MISSING_CASE(x) WARN(1, "Missing switch case (%lu) in %s\n", \
 			     (long) (x), __func__);