ARM: imx: Convert mccmon6 to use DM/DTS in the u-boot proper

This commit converts mccmon6's u-boot proper (in a single commit to avoid
build breaks) to use solely DM/DTS.

The DTS description of the mccmon6 has been ported from Linux kernel
(v4.20, SHA1: 8fe28cb58bcb235034b64cbbb7550a8a43fd88be)

Signed-off-by: Lukasz Majewski <lukma@denx.de>
diff --git a/arch/arm/mach-imx/mx6/Kconfig b/arch/arm/mach-imx/mx6/Kconfig
index 00e3c48..27daf55 100644
--- a/arch/arm/mach-imx/mx6/Kconfig
+++ b/arch/arm/mach-imx/mx6/Kconfig
@@ -232,6 +232,13 @@
 	bool "mccmon6"
 	select MX6QDL
 	select SUPPORT_SPL
+	select DM
+	select DM_GPIO
+	select DM_ETH
+	select DM_SERIAL
+	select DM_I2C
+	select DM_SPI
+	imply CMD_DM
 
 config TARGET_MX6CUBOXI
 	bool "Solid-run mx6 boards"