Add hinted attachment for non-FDT systems. Also, print a message if
setting up the timer fails, because on some types of chips that's the
first attempt to access the device. If the chip is missing/non-responsive
then you'd get a driver that attached and didn't register the rtc, with
no clue about why. On other chip types there are inits that come before
timer setup, and they already print messages about errors.