Add DDR4 init codes, u-boot dtb and defconfig to support DDR4 EVK.
The DDR4 EVK removed eMMC and Flexspi, but use NAND instead. Current
codes support to boot from SD and enable NAND access in regular u-boot.
Signed-off-by: Ye Li <ye.li@nxp.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
Ye Li