pylibfdt: Allow version normalization to fail

In some cases, we might not have the sic portion of setuputils
available. Make our import and use of this be done in try/except blocks
as this is done to suppress a run-time warning that is otherwise
non-fatal.

Reported-by: Pali Rohár <pali@kernel.org>
Fixes: 14165918 ("pylibfdt: Fix disable version normalization")
Signed-off-by: Tom Rini <trini@konsulko.com>