rtc: ftrtc010: let the core handle range

The current range handling is highly suspicious. Anyway, let the core
handle it.
The RTC has a 32 bit counter on top of days + hh:mm:ss registers.

Acked-by: Hans Ulli Kroll <ulli.kroll@googlemail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>