devlink: Add board.serial_number to info subcommand.

devlink: Add board.serial_number to info subcommand.

Add support for reading board serial_number to devlink info
subcommand. Example:

$ devlink dev info pci/0000:af:00.0 -jp
{
    "info": {
        "pci/0000:af:00.0": {
            "driver": "bnxt_en",
            "serial_number": "00-10-18-FF-FE-AD-1A-00",
            "board.serial_number": "433551F+172300000",
            "versions": {
                "fixed": {
                    "board.id": "7339763 Rev 0.",
                    "asic.id": "16D7",
                    "asic.rev": "1"
                },
                "running": {
                    "fw": "216.1.216.0",
                    "fw.psid": "0.0.0",
                    "fw.mgmt": "216.1.192.0",
                    "fw.mgmt.api": "1.10.1",
                    "fw.ncsi": "0.0.0.0",
                    "fw.roce": "216.1.16.0"
                }
            }
        }
    }
}

Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David Ahern <dsahern@kernel.org>