Apple appears to have removed iCloud Keychain support from the iOS 7 Golden Master (GM), which was seeded to developers yesterday. While iCloud preferences previously listed iCloud Keychain, the option has now been removed, suggesting that the initial public release of iOS 7 will not include the function.
This makes sense — it’s a key part of OS X Mavericks as well. No point pushing out a muted feature before that software is released next month. Probably safe to assume it will be a part of iOS 7.1 released alongside new iPads.