benchmarks: Add vgem mmap speed test

Primarily to check that we have the WC read/write disparity.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/benchmarks/Makefile.sources b/benchmarks/Makefile.sources
index bc4f2b5..6865e73 100644
--- a/benchmarks/Makefile.sources
+++ b/benchmarks/Makefile.sources
@@ -19,4 +19,5 @@
 	gem_syslatency			\
 	gem_userptr_benchmark		\
 	kms_vblank			\
+	vgem_mmap			\
 	$(NULL)