[U-Boot] [RFC] Centralise documentation of CONFIG_ options (and finding unused ones)

[Kumar Gala]

>> From this it is easy to find unused options (CONFIG_ARIA is found only as a
> #define in include/configs/aria.h for example)
> 
> So my RFC is twofold:
> 1) Should we start to systematically remove unused options
> 2) Should we centralise all options in a single README (or two, one for
> standard CONFIG options and one for CONFIG_SYS options)?

Can you post data for which options are not used.  While I think automatic removal is harsh, I think something close to automatic is reasonable.

- k