[U-Boot] Add spi nand support in u-boot

[Peter Pan 潘栋 (peterpandong)]

Hi All,

I’d like to add spi nand support in u-boot. But I don’t know where should
the spi nand drivers put in and how to define the architecture.

I find that currently spi_flash in u-boot means spi nor flash. Should I create
a struct spi_nand_flash or make spi_flash compatible?

Thanks
Peter Pan