util-linux: clean up libraries and tools selections

util-linux: clean up libraries and tools selections

Fix several problems in the package recipe:

- Make 'bool "lib<foo>"' the first item in each block
- Move the depends before the selects
- Add missing dependencies on BR2_USE_MMU, for fork()
- Improve help for cramfs utilities and login utilities

Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
[Thomas:
 - remove capitalization of prompts, for consistency
 - add missing dependencies on libsmartcols, and therefore !MMU]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>