tock/tock: Tock 2.1.1

Tock 2.1.1 fixes an issue present in the Tock 2.0 and Tock 2.1 releases concerning system call error return values issued when userspace applications were issuing system calls towards non-existent capsules. Breaking Changes The Tock system call interface specification (TRD 104) mandates that the kernel returns an error of NODEVICE when issuing a system call towards a non-registered driver number. However, Tock 2.0 would instead return an error of NOMEM on a subscribe system call. Furthermore, Tock 2.1 returns an error of NOMEM on all of read-only allow, read-write allow and subscribe system calls. This release changes this behavior and returns an error of NOMEM for all of these cases, in compliance with the specification (https://github.com/tock/tock/pull/3300). All Merged PRs An exhaustive list of all merged pull requests since Tock 2.1: - Prepare for Tock 2.1.1 release tag ([#3361](https://github.com/tock/tock/pull/3361) by [@lschuermann](https://github.com/lschuermann)) - 2.1.1: Fix syscall return codes for wrong driver_number ([#3300](https://github.com/tock/tock/pull/3300) by [@alexandruradovici](https://github.com/alexandruradovici))