CONFIG_RTC_MPC8xx - use internal RTC of MPC8xx
CONFIG_RTC_PCF8563 - use Philips PCF8563 RTC
+ CONFIG_RTC_MC13783 - use MC13783 RTC
CONFIG_RTC_MC146818 - use MC146818 RTC
CONFIG_RTC_DS1307 - use Maxim, Inc. DS1307 RTC
CONFIG_RTC_DS1337 - use Maxim, Inc. DS1337 RTC