microblaze: Enable i2c DM by default

Microblaze has been converted fully to DM that's why enabled DM for I2C
too.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/microblaze-generic_defconfig b/configs/microblaze-generic_defconfig
index df79206..7cf7369 100644
--- a/configs/microblaze-generic_defconfig
+++ b/configs/microblaze-generic_defconfig
@@ -43,6 +43,7 @@
 CONFIG_NETCONSOLE=y
 CONFIG_SPL_DM=y
 CONFIG_XILINX_GPIO=y
+CONFIG_DM_I2C=y
 CONFIG_LED=y
 CONFIG_LED_GPIO=y
 CONFIG_MTD=y