dm: mx6: Move driver model CONFIGs to Kconfig

Remove driver model CONFIGs from the board config headers and use Kconfig
instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/cm_fx6_defconfig b/configs/cm_fx6_defconfig
index 3c0d64f..d2ebf69 100644
--- a/configs/cm_fx6_defconfig
+++ b/configs/cm_fx6_defconfig
@@ -2,3 +2,6 @@
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6QDL,SPL"
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_CM_FX6=y
+CONFIG_DM=y
+CONFIG_DM_GPIO=y
+CONFIG_DM_SERIAL=y
diff --git a/include/configs/cm_fx6.h b/include/configs/cm_fx6.h
index 1f64495..4008306 100644
--- a/include/configs/cm_fx6.h
+++ b/include/configs/cm_fx6.h
@@ -21,13 +21,9 @@
 #define CONFIG_MACH_TYPE		4273
 
 #ifndef CONFIG_SPL_BUILD
-#define CONFIG_DM
-#define CONFIG_CMD_DM
 
-#define CONFIG_DM_GPIO
 #define CONFIG_CMD_GPIO
 
-#define CONFIG_DM_SERIAL
 #define CONFIG_SYS_MALLOC_F_LEN		(1 << 10)
 #endif