rtc: max77686: Add MAX77714 support

The RTC included in the MAX77714 PMIC is very similar to the one in the
MAX77686. Reuse the rtc-max77686.c driver with the minimum required changes
for the MAX77714 RTC.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>