rtc: Add Epson RX8010SJ RTC driver

This driver supports the following functions:
 - reading and setting time
 - alarms when connected to an IRQ
 - reading and clearing the voltage low flags

Datasheet:
http://www.epsondevice.com/docs/qd/en/DownloadServlet?id=ID000956


Signed-off-by: Akshay Bhat <akshay.bhat@timesys.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>