- Recommend mt_st as it is not hard dependency

- fix typos in the description
- add 'Require: mt_st' in order not to surprise users by the missing
'mt' binary

- Disable mt building: this binary from mt_st package offers
advanced capabilities with the same functionality.
- Enable rmt building: 'dump' package no longer include it, besides
cpio code base for rmt is more fresh.
- Reflect those changes in the package description.