Yocto for Pine64

[tkaiser]

It currently just supports pine64 plus but it shouldn't be hard to have it working for Pine64 with 512MB.

All that's needed is to pick the right device tree file in u-boot (important to get Ethernet working since different PHYs and access methods are used). In case you rely on longsleep's u-boot branch it might already work (detection works based on available DRAM size and in case it's 512MB the other .dts will be chosen). As a reference the commit that made this work: https://github.com/longsleep/u-boot-pine...b4e12d2dd0