Kernel: add dynamic RTC functional validation

[Srikanth Muppandam (smuppand)]

Summary

• Add a focused RTC_Validation suite.
• Dynamically discover and select RTC devices.
• Validate RTC time progression through RTC_RD_TIME.
• Validate wake-alarm programming, readback, expiration, and restoration.
• Add guarded RTC_SET_TIME validation with restoration.
• Run full RTC coverage from LAVA YAML.
• Retain runtime inventory, ioctl reports, and kernel-log evidence.

Result handling

• Skip unavailable hardware and optional driver capabilities cleanly.
• Report actionable target prerequisites for failures and skips.
• For rtc-pm8xxx returning ENODEV, report missing DT allow-set-time or persistent NVMEM/UEFI offset storage.
• Do not overwrite an existing active alarm.