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
diff --git a/test/py/tests/test_efi_fit.py b/test/py/tests/test_efi_fit.py
index 4a46438..c836834 100644
--- a/test/py/tests/test_efi_fit.py
+++ b/test/py/tests/test_efi_fit.py
@@ -55,7 +55,7 @@
 
 import os.path
 import pytest
-import u_boot_utils as util
+import utils as util
 
 # Define the parametrized ITS data to be used for FIT images generation.
 ITS_DATA = '''