drm: fix issues with systems with no MTRR

On systems with no MTRR we should still define the interface.

Original bug from apkm.
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/drmP.h

@@ -767,6 +767,20 @@ static inline int drm_mtrr_del(int handle, unsigned long offset,
 
 #else
 #define drm_core_has_MTRR(dev) (0)
+
+#define DRM_MTRR_WC		0
+
+static inline int drm_mtrr_add(unsigned long offset, unsigned long size,
+			       unsigned int flags)
+{
+	return 0;
+}
+
+static inline int drm_mtrr_del(int handle, unsigned long offset,
+			       unsigned long size, unsigned int flags)
+{
+	return 0;
+}
 #endif
 
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