dropbear: update to 2024-86, more options with detailed help

Changes:
- update to 2024-86
- new menuconfig structure
- added in menuconfig almost all available configuration options
- added dependencies for options (some are unavailable on musl)
- added warning messages for invalid config selections
- all options have detailed help descriptions
- removed or replaced all options that required editing sysoptions.h

Signed-off-by: Marius Dinu <[email protected]>