The SH RTC is a BCD RTC with some version having 4 digits for the year.

The range for the RTCs with only 2 digits for the year was unfortunately
shifted to handle 1999 to 2098.
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>