rtc: convert rtc i2c drivers to module_i2c_driver

Factor out some boilerplate code for i2c driver registration into
module_i2c_driver.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Piotr Ziecik <kosmo@semihalf.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Srikanth Srinivasan <srikanth.srinivasan@freescale.com>
Cc: Mike Rapoport <mike@compulab.co.il>
Cc: Sergey Lapin <slapin@ossfans.org>
Cc: Roman Fietze <roman.fietze@telemotive.de>
Cc: Herbert Valerio Riedel <hvr@gnu.org>
Cc: Alexander Bigga <ab@mycable.de>
Cc: Dale Farnsworth <dale@farnsworth.org>
Cc: Gregory Hermant <gregory.hermant@calao-systems.com>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Cc: Martyn Welch <martyn.welch@ge.com>
Cc: Byron Bradley <byron.bbradley@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>