test: Move common FIT code into a separate fit_util file

To avoid duplicating code, create a new fit_util module which provides
various utility functions for FIT. Move this code out from the existing
test_fit.py and refactor it with addition parameters.

Fix up pylint warnings in the conversion.

This involves no functional change.

Signed-off-by: Simon Glass <sjg@chromium.org>
3 files changed