benchmarks: Add simple mmap benchmarks

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/benchmarks/.gitignore b/benchmarks/.gitignore
index 20b390e..2c9d044 100644
--- a/benchmarks/.gitignore
+++ b/benchmarks/.gitignore
@@ -1,4 +1,5 @@
 gem_exec_nop
+gem_mmap
 gem_prw
 gem_userptr_benchmark
 intel_upload_blit_large