drm/i915: Compile-time concatenate WARN_ON macro strings

Using __stringify(x) instead of #x adds support for macros as
a parameter and compile-time concatenation reduces the runtime
overhead.

Slightly increases the .text size but should not matter.

v2:
- Define I915_STATE_WARN_ON though I915_STATE_WARN
  (Bikeshed inspiration by Chris)

v3:
- More specific commit message

v4:
- Do not directly pass arbitary string as format, instead
  guard with "%s" (Dave)

Cc: Rob Clark <robdclark@gmail.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v3)
Acked-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1450441647-23924-3-git-send-email-joonas.lahtinen@linux.intel.comSigned-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -70,11 +70,11 @@
 		BUILD_BUG_ON(__i915_warn_cond); \
 	WARN(__i915_warn_cond, "WARN_ON(" #x ")"); })
 #else
-#define WARN_ON(x) WARN((x), "WARN_ON(%s)", #x )
+#define WARN_ON(x) WARN((x), "%s", "WARN_ON(" __stringify(x) ")")
 #endif
 
 #undef WARN_ON_ONCE
-#define WARN_ON_ONCE(x) WARN_ONCE((x), "WARN_ON_ONCE(%s)", #x )
+#define WARN_ON_ONCE(x) WARN_ONCE((x), "%s", "WARN_ON_ONCE(" __stringify(x) ")")
 
 #define MISSING_CASE(x) WARN(1, "Missing switch case (%lu) in %s\n", \
 			     (long) (x), __func__);
@@ -94,14 +94,8 @@
 	unlikely(__ret_warn_on);					\
 })
 
-#define I915_STATE_WARN_ON(condition) ({				\
-	int __ret_warn_on = !!(condition);				\
-	if (unlikely(__ret_warn_on))					\
-		if (!WARN(i915.verbose_state_checks,			\
-			  "WARN_ON(" #condition ")\n"))			\
-			DRM_ERROR("WARN_ON(" #condition ")\n");		\
-	unlikely(__ret_warn_on);					\
-})
+#define I915_STATE_WARN_ON(x)						\
+	I915_STATE_WARN((x), "%s", "WARN_ON(" __stringify(x) ")")
 
 static inline const char *yesno(bool v)
 {