rtc: New driver for RTC in Netronix embedded controller

With this driver, mainline Linux can keep its time and date in sync with
the vendor kernel.

Advanced functionality like alarm and automatic power-on is not yet
supported.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>