rtc: pcf8563: let the core handle range offsetting

Set the RTC range properly and use the core windowing and offsetting to
(unfortunately) map back to a 1970-2069 range.

Link: https://lore.kernel.org/r/20190829212547.19185-5-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>