rtc: Add support for the rtc found in the MC13892 PMIC

The mfd driver for MC13783 recently got support for MC13892 and was
renamed accordingly from mc13783-core to mc13xxx-core.  Do the same for
rtc-mc13783.

The only relevant change is to use platform id's to tell the platform bus
that this driver is responsible for mc13892-rtc devices, too.

Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>