dt-bindings: rtc: sprd,sc2731-rtc: convert to YAML

Convert the Spreadtrum SC2731 RTC bindings to DT schema.
Rename file to match compatible.

Signed-off-by: Stanislav Jakubek <stano.jakubek@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/ZolsyEC8eeJWNIb6@standask-GA-A55M-S2HP


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