tools: ynl: allow passing binary data

Recent changes made us assume that input for binary data is in hex.
When using YNL as a Python library it's possible to pass in raw bytes.
Bring the ability to do that back.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20230824003056.1436637-2-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>