gpiolib: of: add a quirk for legacy names in MOXA ART RTC

The driver is using non-standard "gpio-rtc-data", "gpio-rtc-sclk", and
"gpio-rtc-reset" names for properties describing its gpios. In
preparation to converting to the standard naming ("rtc-*-gpios") and
switching the driver to gpiod API add a quirk to gpiolib to keep
compatibility with existing DTSes.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>