rtc: sirfsoc: set range

This RTC is a 32bit counter running at 16Hz. This overflows every eight
years and a half. However, the driver uses the SW_VALUE register to store
the overflow, extending the counter to 64bit as long as the update happens
before the overflow.

Link: https://lore.kernel.org/r/20200305160452.27808-2-alexandre.belloni@bootlin.com


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