mlxsw: core: Add support for devlink info command

Expose the following ASIC information via devlink info command:
  - Driver name
  - Hardware revision
  - Firmware PSID
  - Running firmware version

Standard output example:
  $ devlink dev info pci/0000:03:00.0
  pci/0000:03:00.0:
    driver mlxsw_spectrum
    versions:
        fixed:
          hw.revision A0
          fw.psid MT_2750110033
        running:
          fw.version 13.1910.622

Signed-off-by: Shalom Toledo <shalomt@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>