Although the shipping kernel-config with genkernel has ~10 of these various RTC hardware drivers marked as modules, the resulting built kernel & initramfs has these things disabled. Here's an excerpt from arch/x86_64/kernel-config:
The problem is that CONFIG_RTC_CLASS is a boolean, not tristate, so =m is not valid, and so all things depending on RTC_CLASS get dropped from the config. Changing this to CONFIG_RTC_CLASS=y should fix the issue, I have tested this locally with success.
*** This bug has been marked as a duplicate of bug 444932 ***