buildman: Replace the Options column with config name

This appears in boards.cfg but we want to remove it. Drop support for
generating it and reading it. Detect an old boards.cfg file that has
this field and regenerate it, to avoid problems.

Instead, add the config name in that place. This fixes a subtle bug in
the generation code, since it uses 'target' for the config name and then
overwrites the value in scan() by setting params['target'] to the name
of the defconfig. The defconfig name is not the same as the
SYS_CONFIG_NAME variable.

With this change, we still have the config name and it can be searched
by buildman, e.g. with:

   buildman -nv sun5i

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Tom Rini <trini@konsulko.com>