rtc: Fix module autoload for OF platform drivers

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

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>