rtc: s5m: Move enum from rtc.h to rtc-s5m.c

Move this enum to rtc-s5m.c once it is meaningless to others drivers [1].

[1] https://marc.info/?l=linux-rtc&m=152060068925948&w=2



Suggested-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>