binman: Move compression bintools creation into test setup

Move compression bintools (packer) creation into test setup to reuse
bintool objects between tests.

Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier@weidmueller.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Put comp_util import back in, since it is still needed here:
Signed-off-by: Simon Glass <sjg@chromium.org>
1 file changed