Migrate .mlirbc and .irpa files into Git LFS. (#147)

Follow-up to
#126 (comment)

All I needed to do for generating this PR was pull changes (having git
lfs installed). I think to avoid this in the future, others working with
these files should also install git lfs.

iree_tests/README.md

@@ -41,6 +41,13 @@ with `.mlir` files and native (C/C++) tools. Each test suite or test case may
 also have its own import logic, with all test suites converging onto the
 standard format described above.
 
+Some large files are stored using [Git LFS](https://git-lfs.com/). When working
+with these files please ensure that you have Git LFS installed:
+
+```bash
+$ git lfs install
+```
+
 ## Running tests
 
 Tests are run using the [pytest](https://docs.pytest.org/en/stable/) framework.