When the RTC block looses power it needs a reset sequence to make it
usable again. Otherwise, writes to the time register have no effect.

This reset sequence combines information from the mvebu_rtc driver in
the Marvell provided U-Boot, and the SolidRun provided U-Boot repo.

Tested on the Armada 388 based SolidRun Clearfog Base.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>