rtc: ingenic: Only support probing from devicetree

With the recent work on supporting Device Tree on Ingenic SoCs, no
driver ever probes from platform code anymore, so we can clean a bit
this driver by removing the non-devicetree paths.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200505221336.222313-1-paul@crapouillou.net


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>