devlink: add info subcommand

devlink: add info subcommand

Add support for reading the device serial number, driver name
and various versions.  Example:

$ devlink dev info pci/0000:82:00.0
pci/0000:82:00.0:
  driver nfp
  serial_number 16240145
  versions:
      fixed:
        board.id AMDA0081-0001
        board.rev 15
        board.vendor SMA
        board.model hydrogen
      running:
        fw.mgmt 010181.010181.0101d4
        fw.cpld 0x1030000
        fw.app abm-d372b6
        fw.undi 0.0.2
        chip.init AMDA-0081-0001  20160318164536
      stored:
        fw.mgmt 010181.010181.0101d4
        fw.app abm-d372b6
        fw.undi 0.0.2
        chip.init AMDA-0081-0001  20160318164536

$ devlink -jp dev info pci/0000:82:00.0
{
    "info": {
        "pci/0000:82:00.0": {
            "driver": "nfp",
            "serial_number": "16240145",
            "versions": {
                "fixed": {
                    "board.id": "AMDA0081-0001",
                    "board.rev": "15",
                    "board.vendor": "SMA",
                    "board.model": "hydrogen"
                },
                "running": {
                    "fw.mgmt": "010181.010181.0101d4",
                    "fw.cpld": "0x1030000",
                    "fw.app": "abm-d372b6",
                    "fw.undi": "0.0.2",
                    "chip.init": "AMDA-0081-0001  20160318164536"
                },
                "stored": {
                    "fw.mgmt": "010181.010181.0101d4",
                    "fw.app": "abm-d372b6",
                    "fw.undi": "0.0.2",
                    "chip.init": "AMDA-0081-0001  20160318164536"
                }
            }
        }
    }
}

v5:
 - remove spurious new line.
v4:
 - more commit message improvements.
v3:
 - show up-to-date output in the commit message.
v2 (Jiri):
 - remove filtering;
 - add example in the commit message.
RFCv2:
 - make info subcommand of dev.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David Ahern <dsahern@gmail.com>