configs: kirkwood: Move RTC_MV to DM and Kconfig

Now that there is DM support in the RTC_MV driver update board configs
to use it.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/configs/SBx81LIFKW_defconfig b/configs/SBx81LIFKW_defconfig
index 348f861..c786120 100644
--- a/configs/SBx81LIFKW_defconfig
+++ b/configs/SBx81LIFKW_defconfig
@@ -35,5 +35,7 @@
 CONFIG_MV88E61XX_CPU_PORT=10
 CONFIG_MV88E61XX_PHY_PORTS=0x003
 CONFIG_MV88E61XX_FIXED_PORTS=0x300
+CONFIG_DM_RTC=y
+CONFIG_RTC_MV=y
 CONFIG_SPI=y
 CONFIG_KIRKWOOD_SPI=y