Cubox-i and Hummingboard support several MX6 SoCs: mx6solo, mx6dual-lite,
mx6dual and mx6quad. Add support for the different SoC/memory sizes
combinations.
DDR initialization values were extracted from Solid-run internal U-boot.
Tested on a CuBox-i4Pro, HummingBoard-i2eX and HummingBoard-i1.