viatool: add NetBSD support

Change-Id: I033044e4b781475d6d60a49a61313a720103ce38
Signed-off-by: Andrey Korolyov <andrey@xdel.ru>
Reviewed-on: https://review.coreboot.org/12836
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
3 files changed