mlxsw: core_linecards: Expose device PSID over device info

Use tunneled MGIR to obtain PSID of line card device and extend
device_info_get() op to fill up the info with that.

Example:

$ devlink dev info auxiliary/mlxsw_core.lc.0
auxiliary/mlxsw_core.lc.0:
  versions:
      fixed:
        hw.revision 0
        fw.psid MT_0000000749
      running:
        ini.version 4
        fw 19.2010.1312

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>