[U-Boot] Improvements to Rock960

Hi,

Some improvements to the Rock960, tested locally on a v1.2 board. Most are self explanatory in the patches.

The usb3 enablement requires the dwc3 patch series [1] that Mark posted to actually work but is completely indendent of it.

Peter

[1] http://patchwork.ozlabs.org/project/uboot/list/?series=116911