devlink: Add port param get command

Add port param get command which gets data per parameter.
It also has option to dump the parameters data per port.

v7->v8: Append "Acked-by: Jiri Pirko <jiri@mellanox.com>"

Cc: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>