ANDROID: rtc: class: support hctosys from modular RTC drivers

In order to support setting the system time from modular RTC drivers
via the hctosys mechanism, check at the end of RTC device registration
for whether the time should be synced, rather than once at late init.

Bug: 144103362
Bug: 143046457
Change-Id: I65d2fd14e075a65f2a23e1268b02c907c5245fb8
Signed-off-by: Steve Muckle <smuckle@google.com>