RTC: sa1100: support sa1100, pxa and mmp soc families

Since the regmap of rtc on sa1100, pxa and mmp Marvell soc families are
almost the same, so re-arch the rtc-sa1100 to support them.

Signed-off-by: Jett.Zhou <jtzhou@marvell.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>