Register dmutc UTC library

[JaxCalder]

Register dmutc as a platform-independent Library module. UTC uses the generic RTC VFS interface; dmdevfs reports class=rtc and a packaged libsystemd rule starts a type=library unit with the actual device path. No hardware port, driver registration or hardcoded source path.

Publish this registry entry after the initial dmutc release, which depends on the new public libsystemd lifecycle header. Source module dependencies remain unversioned; package resolution selects versions.

Validation of the implementation: STM32F746G-DISCO automatic service start after reset; UTC 6/6, RTC 12/12, RNG 6/6. Native tests and M4/M7 builds also pass; evidence in dmutc docs/testing.md.

Related implementation PRs:

• RTC reporting: Report RTC devices to libsystemd for device rules dmdevfs#73
• Generic library service lifecycle: Support per-unit lifecycle callbacks for library services dmsystem#8
• UTC library: Implement UTC library with rule-driven RTC services dmutc#1
• Boot configuration: Install rule-driven UTC library service configuration dmod-boot#132
• Ecosystem: Integrate RTC reporting and rule-driven UTC library services dmod-ecosystem#31
• Registry: Register dmutc UTC library #17