patman: Avoid using func_test at top level

Import this only when it is needed, since it is not present when
installed via 'pip install'.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: https://source.denx.de/u-boot/u-boot/-/issues/26
diff --git a/tools/patman/__main__.py b/tools/patman/__main__.py
index 3ca858c..d53f686 100755
--- a/tools/patman/__main__.py
+++ b/tools/patman/__main__.py
@@ -24,7 +24,6 @@
 # Our modules
 from patman import cmdline
 from patman import control
-from patman import func_test
 from u_boot_pylib import terminal
 from u_boot_pylib import test_util
 from u_boot_pylib import tools