Rename mc13783-rtc so that it can be used for both MC13783 and MC13892 PMICs.

efikamx board, for example, does use a MC13892 PMIC, but the RTC selection is currently made as:

#define CONFIG_RTC_MC13783

,which is not very obvious.

Let the MC13783 and MC13892 RTC be selected by:

#define CONFIG_RTC_MC13XXX

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Stefano Babic <sbabic@denx.de>