rtc: driver for Cortina Gemini

Driver for the on chip RTC found on Cortina's SoC Gemini.

Signed-off-by: Hans Ulli Kroll <ulli.kroll@googlemail.com>
[alexandre.belloni@free-electrons.com: use devm_request_irq() and remove
useless goto]
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>