rtc: rx8010: switch to using the preferred RTC API

Use devm_rtc_allocate_device() + rtc_register_device() instead of the
deprecated devm_rtc_device_register().

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200914154601.32245-12-brgl@bgdev.pl