benchmarks: Add a set-domain benchmark

Benchmark the overhead of changing from GTT to CPU domains and vice
versa. Effectively this measures the cost of a clflush, and how well the
driver can avoid them.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/benchmarks/Makefile.sources b/benchmarks/Makefile.sources
index 453f223..fd81195 100644
--- a/benchmarks/Makefile.sources
+++ b/benchmarks/Makefile.sources
@@ -13,6 +13,7 @@
 	gem_exec_trace			\
 	gem_mmap			\
 	gem_prw				\
+	gem_set_domain			\
 	gem_userptr_benchmark		\
 	gem_wait				\
 	kms_vblank			\