imx: Add i.MX8MM EVK board support.

Add board and SoC dts
Add ddr training code
support SD/MMC/GPIO/PINCTRL/UART

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8m/Kconfig b/arch/arm/mach-imx/imx8m/Kconfig
index 35c978e..f520075 100644
--- a/arch/arm/mach-imx/imx8m/Kconfig
+++ b/arch/arm/mach-imx/imx8m/Kconfig
@@ -24,8 +24,15 @@
 	select IMX8MQ
 	select IMX8M_LPDDR4
 
+config TARGET_IMX8MM_EVK
+	bool "imx8mm LPDDR4 EVK board"
+	select IMX8MM
+	select SUPPORT_SPL
+	select IMX8M_LPDDR4
+
 endchoice
 
 source "board/freescale/imx8mq_evk/Kconfig"
+source "board/freescale/imx8mm_evk/Kconfig"
 
 endif