rtc: rtc-mxc: convert to module_platform_driver

Converting to module_platform_driver can make the code smaller and cleaner.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>