tools: ynl-gen: refactor check validation for TypeBinary

We only support a single check at a time for TypeBinary.
Refactor the code to cover 'exact-len' and make adding
new checks easier.

Link: https://lore.kernel.org/20241004063855.1a693dd1@kernel.org
Link: https://patch.msgid.link/20241007155311.1193382-1-kuba@kernel.org


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