[U-Boot] [PATCH] cmd_onenand.c: moved to standard subcommand handling

[Frans Meulenbroeks]

Forgot this disclaimer, thought I added it, sry.

NOTE:
This code is untested as I have no board with onenand support.
However, it compiles properly (tested by building opap3_evm, which uses this).
The changes I did are purely splitting do_onenand in separate
functions and add the subcommand parsing (which itself was taken from
i2c, on which I tested it before).
So I do not expect any serious issues, but I would suggest testing
this before integrating it.

Best regards, Frans