test/py: Drop u_boot_ prefix on test files

We know this is U-Boot so the prefix serves no purpose other than to
make things longer and harder to read. Drop it and rename the files.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # test_android / test_dfu

test/py/tests/test_ofplatdata.py

@@ -2,7 +2,7 @@
 # Copyright (c) 2016 Google, Inc
 
 import pytest
-import u_boot_utils as util
+import utils as util
 
 @pytest.mark.boardspec('sandbox_spl')
 @pytest.mark.buildconfigspec('spl_of_platdata')