Some code that runs at VFS_MOUNT() time (explained in the follow-up)
may benefit from having reasonable timestamps if we can offer them. The
existing inittodr() implementation won't touch the clock if we did get
a good time from the RTC, so we'll move the attempt to set the RTC up
in a subsequent change, and fallback to using time from the fs if we
still need to.
The KPI here was designed to try and avoid losing some flexibility from
inittodr(); the cookie is larger than it needs to be in case we want to
pass more context between the two calls later, but it's only used now
to indicate that we actually set the time.