#133 U-Boot fixes for osboot merge, and more

Here's another batch of patches for U-Boot integration. Major points: - Fixes for things that's broken since the osboot merge - Use coreboot crossgcc to build U-Boot - Common tree for U-Boot builds - U-Boot as payload for qemu_x86_12mb - New qemu_arm64_12mb board with only U-Boot - Some of the missing scripts I'm not sure I'll stop here, but at least wanted to send it in case I get interrupted by other things. (Also need to write stuff for lbwww, I know).