rtc: Make mc13783-rtc driver generic

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>
diff --git a/README b/README
index c05c40a..46f062f 100644
--- a/README
+++ b/README
@@ -876,7 +876,7 @@
 
 		CONFIG_RTC_MPC8xx	- use internal RTC of MPC8xx
 		CONFIG_RTC_PCF8563	- use Philips PCF8563 RTC
-		CONFIG_RTC_MC13783	- use MC13783 RTC
+		CONFIG_RTC_MC13XXX	- use MC13783 or MC13892 RTC
 		CONFIG_RTC_MC146818	- use MC146818 RTC
 		CONFIG_RTC_DS1307	- use Maxim, Inc. DS1307 RTC
 		CONFIG_RTC_DS1337	- use Maxim, Inc. DS1337 RTC