rtc: ds1672, max6900, max8998: Add MODULE_DEVICE_TABLE

The device table is required to load modules based on modaliases.
After adding MODULE_DEVICE_TABLE, below entries will be added to
modules.alias:

alias i2c:ds1672 rtc_ds1672
alias i2c:max6900 rtc_max6900
alias platform:lp3974-rtc rtc_max8998
alias platform:max8998-rtc rtc_max8998

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Dale Farnsworth <dale@farnsworth.org>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-ds1672.c

@@ -198,6 +198,7 @@ static struct i2c_device_id ds1672_id[] = {
 	{ "ds1672", 0 },
 	{ }
 };
+MODULE_DEVICE_TABLE(i2c, ds1672_id);
 
 static struct i2c_driver ds1672_driver = {
 	.driver = {

drivers/rtc/rtc-max6900.c

@@ -234,6 +234,7 @@ static struct i2c_device_id max6900_id[] = {
 	{ "max6900", 0 },
 	{ }
 };
+MODULE_DEVICE_TABLE(i2c, max6900_id);
 
 static struct i2c_driver max6900_driver = {
 	.driver = {

drivers/rtc/rtc-max8998.c

@@ -309,6 +309,7 @@ static const struct platform_device_id max8998_rtc_id[] = {
 	{ "lp3974-rtc", TYPE_LP3974 },
 	{ }
 };
+MODULE_DEVICE_TABLE(platform, max8998_rtc_id);
 
 static struct platform_driver max8998_rtc_driver = {
 	.driver		= {