rtc: add armada38x driver

Add RTC driver for Armada 38x, based on Linux' driver.
For now implement only `marvell,armada-380-rtc` compatible.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
Cc: Pali Rohár <pali@kernel.org>
Cc: Baruch Siach <baruch@tkos.co.il>
Cc: Chris Packham <judge.packham@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Pali Rohár <pali@kernel.org>
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index aa6d901..dafba35 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -38,6 +38,13 @@
 	   Some real-time clocks support the output of 32kHz square waves (such as ds3231),
 	   the config symbol choose Real Time Clock device 32Khz output feature.
 
+config RTC_ARMADA38X
+	bool "Enable Armada 38x Marvell SoC RTC"
+	depends on DM_RTC && ARCH_MVEBU
+	help
+	  This adds support for the in-chip RTC that can be found in the
+	  Armada 38x Marvell's SoC devices.
+
 config RTC_PCF2127
 	bool "Enable PCF2127 driver"
 	depends on DM_RTC