[U-Boot] [v3 (RFC)] Proposal to add NAND-boot support for Sunxi SPL

Hereby a v3 of the patches adding NAND support to SPL. Most noticably all the feedback has been addressed: tidy structs for NAND and DMA, timeouts on wait operations and more proper use of the CCU. Patches are marked RFC mostly because I'm still contemplating the implementation of a proper full NAND driver to be used with the existing UBI subsystem. This could mean some slight changes in structure to better accomodate code sharing between sunxi-nand for SPL and U-boot. If you wish you can merge the first three patches though, I expect them not to change any further. Thanks for earlier feedback, and don't hesitate to let me know if anything else could be improved. Cheers,

Roy