rtc: imxdi: add the unit recovery code

This code is required to recover the unit from a security violation.
Hopefully this code can recover the unit from a hardware related invalid
state as well.

Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Signed-off-by: Robert Schwebel <rsc@pengutronix.de>
[rsc: got NDA clearance from Freescale]
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>