ARM: imx6: Add DHCOM i.MX6 PDK board support

Add support for the DHCOM i.MX6 PDK board. This board has:
- FEC ethernet
- EHCI USB host
- 3x SDMMC

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Stefano Babic <sbabic@denx.de>

configs/dh_imx6_defconfig

@@ -0,0 +1,51 @@
+CONFIG_ARM=y
+CONFIG_ARCH_MX6=y
+CONFIG_SPL_GPIO_SUPPORT=y
+CONFIG_SPL_LIBCOMMON_SUPPORT=y
+CONFIG_SPL_LIBGENERIC_SUPPORT=y
+CONFIG_MX6_DDRCAL=y
+CONFIG_TARGET_DHCOMIMX6=y
+CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SPI_FLASH_SUPPORT=y
+CONFIG_SPL_SPI_SUPPORT=y
+CONFIG_SPL_WATCHDOG_SUPPORT=y
+CONFIG_FIT=y
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg,MX6QDL"
+CONFIG_BOOTDELAY=3
+CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
+CONFIG_SPL=y
+CONFIG_SPL_I2C_SUPPORT=y
+CONFIG_HUSH_PARSER=y
+CONFIG_CMD_BOOTZ=y
+# CONFIG_CMD_IMLS is not set
+CONFIG_CMD_MEMTEST=y
+CONFIG_CMD_UNZIP=y
+# CONFIG_CMD_FLASH is not set
+CONFIG_CMD_GPIO=y
+CONFIG_CMD_I2C=y
+CONFIG_CMD_MMC=y
+CONFIG_CMD_PART=y
+CONFIG_CMD_SATA=y
+CONFIG_CMD_SF=y
+CONFIG_CMD_USB=y
+CONFIG_CMD_DHCP=y
+CONFIG_CMD_MII=y
+CONFIG_CMD_PING=y
+CONFIG_CMD_CACHE=y
+CONFIG_CMD_TIME=y
+CONFIG_CMD_EXT2=y
+CONFIG_CMD_EXT4=y
+CONFIG_CMD_EXT4_WRITE=y
+CONFIG_CMD_FAT=y
+CONFIG_CMD_FS_GENERIC=y
+CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
+CONFIG_PHYLIB=y
+CONFIG_PHY_MICREL=y
+CONFIG_PHY_MICREL_KSZ90X1=y
+CONFIG_NETDEVICES=y
+CONFIG_FEC_MXC=y
+CONFIG_USB=y
+CONFIG_USB_STORAGE=y
+CONFIG_OF_LIBFDT=y