rtc: s5m: Drop S5M8763 support

The S5M8763 MFD has no device tree compatible, and since board file
support for it was removed, there's no way to use this MFD. After
removing the remaining code for it from the MFD driver, also remove
support for it in the s5m RTC driver, and all remaining references to
it.

Signed-off-by: David Virag <virag.david003@gmail.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230131183008.4451-3-virag.david003@gmail.com