rtc: Add DM support to ds1307

Add an implementation of the ds1307 driver that uses the driver model
i2c APIs.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index cb79a01..d06130c7 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -23,4 +23,11 @@
 	  has a selectable I2C-bus or SPI-bus, a backup battery switch-over circuit, a
 	  programmable watchdog function, a timestamp function, and many other features.
 
+config RTC_DS1307
+	bool "Enable DS1307 driver"
+	depends on DM_RTC
+	help
+	  Support for Dallas Semiconductor (now Maxim) DS1307 and DS1338/9 and
+	  compatible Real Time Clock devices.
+
 endmenu