binman: Move to absolute imports

At present binman sets the python path on startup so that it can access
the libraries it needs. If we convert to use absolute imports this is not
necessary.

Move binman to use absolute imports. This enables removable of the path
adjusting in Entry also.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/elf_test.py b/tools/binman/elf_test.py
index ac26fd5..e4497f3 100644
--- a/tools/binman/elf_test.py
+++ b/tools/binman/elf_test.py
@@ -10,8 +10,8 @@
 import tempfile
 import unittest
 
+from binman import elf
 import command
-import elf
 import test_util
 import tools
 import tout