dm: rtc: Add a uclass for real-time clocks

Add a uclass for real-time clocks which support getting the current time,
setting it and resetting the chip to a known-working state. Some RTCs have
additional registers which can be used to store settings, so also provide
an interface to these.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index e69de29..bd63621 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -0,0 +1,8 @@
+config DM_RTC
+	bool "Enable Driver Model for RTC drivers"
+	depends on DM
+	help
+	  Enable drver model for real-time-clock drivers. The RTC uclass
+	  then provides the rtc_get()/rtc_set() interface, delegating to
+	  drivers to perform the actual functions. See rtc.h for a
+	  description of the API.