Board serial number is a serial number, often available in PCI
*Vital Product Data*.

Also, update devlink-info.rst documentation file.

Cc: Jiri Pirko <jiri@mellanox.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: NVasundhara Volam <vasundhara-v.volam@broadcom.com>
Reviewed-by: NMichael Chan <michael.chan@broadcom.com>
Reviewed-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>