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_vbe_vpl.py b/test/py/tests/test_vbe_vpl.py
index 1138917..317a324 100644
--- a/test/py/tests/test_vbe_vpl.py
+++ b/test/py/tests/test_vbe_vpl.py
@@ -6,7 +6,7 @@
 import os
 
 import pytest
-import u_boot_utils
+import utils
 
 @pytest.mark.boardspec('sandbox_vpl')
 @pytest.mark.requiredtool('dtc')
@@ -19,13 +19,13 @@
 
     # Enable firmware1 and the mmc that it uses. These are needed for the full
     # VBE flow.
-    u_boot_utils.run_and_log(
+    utils.run_and_log(
         cons, f'fdtput -t s {fdt} /bootstd/firmware0 status disabled')
-    u_boot_utils.run_and_log(
+    utils.run_and_log(
         cons, f'fdtput -t s {fdt} /bootstd/firmware1 status okay')
-    u_boot_utils.run_and_log(
+    utils.run_and_log(
         cons, f'fdtput -t s {fdt} /mmc3 status okay')
-    u_boot_utils.run_and_log(
+    utils.run_and_log(
         cons, f'fdtput -t s {fdt} /mmc3 filename {image_fname}')
 
     # Remove any existing RAM file, so we don't have old data present