The RTC device that will be used to (re)initialize the system
clock, usually rtc0. Initialization is done when the system
starts up, and when it resumes from a low power state. This
device should record time in UTC, since the kernel won't do
timezone correction.

The driver for this RTC device must be loaded before late_initcall
functions run, so it must usually be statically linked.

This clock should be battery-backed, so that it reads the correct
time when the system boots from a power-off state. Otherwise, your
system will need an external clock source (like an NTP server).

If the clock you specify here is not battery backed, it may still
be useful to reinitialize system time when resuming from system
sleep states. Do not specify an RTC here unless it stays powered
during all this system's supported sleep states.