power_supply: Convert drivers/power/* to use module_platform_driver()

This patch converts the drivers in drivers/power/* to use the
module_platform_driver() macro which makes the code smaller and a bit
simpler.

Cc: Mike Rapoport <mike@compulab.co.il>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Nithish Mahalingam <nithish.mahalingam@intel.com>
Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Cc: Haojian Zhuang <haojian.zhuang@marvell.com>
Cc: Balaji Rao <balajirrao@openmoko.org>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Clifton Barnes <cabarnes@indesign-llc.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>

drivers/power/wm831x_backup.c

@@ -226,17 +226,7 @@ static struct platform_driver wm831x_backup_driver = {
 	},
 };
 
-static int __init wm831x_backup_init(void)
-{
-	return platform_driver_register(&wm831x_backup_driver);
-}
-module_init(wm831x_backup_init);
-
-static void __exit wm831x_backup_exit(void)
-{
-	platform_driver_unregister(&wm831x_backup_driver);
-}
-module_exit(wm831x_backup_exit);
+module_platform_driver(wm831x_backup_driver);
 
 MODULE_DESCRIPTION("Backup battery charger driver for WM831x PMICs");
 MODULE_AUTHOR("Mark Brown <broonie@opensource.wolfsonmicro.com>");