add export utils to example targets (#228)

Summary:
Pull Request resolved: #228

as title

exporting via buck currently doesn't work without adding the following target dep

Reviewed By: guangy10

Differential Revision: D48992398

fbshipit-source-id: 2a8327e5edae716c711c7014288a28aad4b981c2

Author: mcr229

examples/backend/targets.bzl

@@ -24,6 +24,7 @@ def define_common_targets():
             "//executorch/backends/xnnpack/partition:xnnpack_partitioner",
             "//executorch/examples/recipes/xnnpack_optimization:models",
             "//executorch/examples/quantization:quant_utils",
+            "//executorch/examples/export:utils",
             "//executorch/exir:lib",
             "//executorch/exir/backend:backend_api",
         ],