devlink: Force enclosing array on binary fmsg data

Add a new API for start/end binary array brackets [] to force array
around binary data as required from JSON. With this restriction, re-open
API to set binary fmsg data.

Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>