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_net_boot.py b/test/py/tests/test_net_boot.py
index d023080..abf6dfb 100644
--- a/test/py/tests/test_net_boot.py
+++ b/test/py/tests/test_net_boot.py
@@ -2,7 +2,7 @@
 # (C) Copyright 2023, Advanced Micro Devices, Inc.
 
 import pytest
-import u_boot_utils
+import utils
 import test_net
 import re
 
@@ -130,7 +130,7 @@
     setup_networking(ubman)
     addr = f.get('addr', None)
     if not addr:
-        addr = u_boot_utils.find_ram_base(ubman)
+        addr = utils.find_ram_base(ubman)
 
     fn = f['fn']
     timeout = f.get('timeout', 50000)