[U-Boot] Removing the need for boards.cfg

[Simon Glass]

Hi,

At present, as a work-around, we generate boards.cfg if needed. This
is quite a slow process since each board config must be fully
processed.

What can we do to improve this? We only need a small number of options
in order to start buildman - things like CONFIG_SYS_ARCH,
CONFIG_SYS_CPU, etc.

I wonder if we could run a script which adds these to the defconfigs
for each board and then apply a patch to mainline? Would that require
removing the options from the config.h files? Or could we do that
later as a separate step?

Regards,
Simon