rtc-ds1307: oscillator restart for ds13{37,38,39,40}

When we find a ds1337 or ds1339 with the oscillator powered off, turn it
on.  If the oscillator fault flag was set, clear it and warn that the clock
needs to be set.

David Brownell: Bugfixes; provide corresponding update for ds1338, and the
core of the fix for ds1340.  Use a common warning message ("SET TIME!")
whenever the clock needs to be set after oscillator fault (or oscillator
enable, if fault is not a separate status).

Signed-off-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>