rtc: Enable compile testing for Maxim and Samsung drivers

max8907, max77686 and s5m RTC drivers can be compile tested to increase
build coverage.  The s5m-rtc uses REGMAP_IRQ so add this as explicit
dependency.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>