rtc: snvs: set range

The SNVS is a 47-bit counter incremented at 32768Hz, it is then a 32-bit
second counter.

Link: https://lore.kernel.org/r/20190828205056.31321-1-alexandre.belloni@bootlin.com


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