rtc: davinci: let the core handle rtc range

rtc: davinci: let the core handle rtc range

Let the core handle offsetting and windowing the RTC range.

This rtc has hours, minutes, seconds and 16bit days. As the driver has the
RTC epoch set to year 2000, this means that the end of the range is 2^16
days minus one second later. This is Sun Jun  6 23:59:59 UTC 2179. This
is better than the currently set year 2099.

Link: https://lore.kernel.org/r/20200305215022.32533-3-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>