siemens/mc_bdx1: Add usage of external RTC PCF8523

This mainboard contains an external RTC chip PCF8523. Enable usage of
this chip and add some initialization values to device tree.

Change-Id: I25c0a017899ee904f3aa02bdc7dcaf61dee67e3a
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/15642
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/mainboard/siemens/mc_bdx1/Kconfig b/src/mainboard/siemens/mc_bdx1/Kconfig
index 960fe00..e679eb5 100644
--- a/src/mainboard/siemens/mc_bdx1/Kconfig
+++ b/src/mainboard/siemens/mc_bdx1/Kconfig
@@ -12,6 +12,7 @@
 	select USE_SIEMENS_HWILIB
 	select DRIVER_INTEL_I210
 	select DRIVER_SIEMENS_NC_FPGA
+	select DRIVERS_I2C_PCF8523
 
 config MAINBOARD_DIR
 	string