rtc: s3c: Disable all enable (RTC, tick) bits in the probe

Bootloader might use RTC hardware and leave it in the enabled state. Ensure
that the potentially enabled periodic tick interrupts are disabled before
enabling the driver, because they might cause lockup if tick interrupt
happens after disabling RTC gate clock.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201202111318.5353-1-m.szyprowski@samsung.com