[libmultipath] embed a struct dm_info pointer in struct multipath

[libmultipath] embed a struct dm_info pointer in struct multipath

- replace dm_get_state() by a generic dm_get_info()
- move mpp->minor users to mpp->dmi->minor
- move mpp->dmstate users to mpp->dmi->suspended
- cli handlers for resume/suspend map now trigger dm_get_info()
  instead of playing directly with mpp->dmstate : more reliable