rtc: Fix module autoload for rtc-{ab8500,max8997,s5m} drivers

These platform drivers have a platform device ID table but the module
alias information is not created so module autoloading will not work.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>