rtc: add rv3029c2 RTC support

Add support for the Micro Crystal RV3029-C2 RTC chips.

Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Gregory Hermant <gregory.hermant@calao-systems.com>
Cc: Wan ZongShun <mcuos.com@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>