fru: Add decoder for multirec system mgmt records

* Add a decoder for System Management records in
  the Multirecord area
* Refactor GUID/UUID decoding: Use the same code for `mc guid`
  and for `fru print` to decode the GUID and System Unique ID
  in System Management records in the Multirecord Area.
* Fix some type errors in calls to printf/sprintf in GUID decoder

Signed-off-by: Alexander Amelkin <alexander@amelkin.msk.ru>