scripts: utils: posix: add dry-run option and improve logging

Add a `--dry-run` (or `-d`) option to the posix kconfig
migration script for deprecated POSIX Kconfigs.

Additionally, add a set of skipped options (e.g. `TIMER`).

The `CONFIG_TIMER` option does not exist in the tree anymore
and was way too generically named previously, so the false
positive rate is astronomical, so it makes sense to skip it.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>