drm/radeon: Only prompt for enabling PAT when we'd allow write-combining

No use bothering users about this for whom we disable write-combining for
other reasons anyway.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_object.c

@@ -241,6 +241,7 @@ int radeon_bo_create(struct radeon_device *rdev,
 #warning Please enable CONFIG_MTRR and CONFIG_X86_PAT for better performance \
 	 thanks to write-combining
 
+	if (bo->flags & RADEON_GEM_GTT_WC)
 		DRM_INFO_ONCE("Please enable CONFIG_MTRR and CONFIG_X86_PAT for "
 			      "better performance thanks to write-combining\n");
 	bo->flags &= ~(RADEON_GEM_GTT_WC | RADEON_GEM_GTT_UC);