Kconfig: add CONFIG_BROKEN

Provide a Kconfig option that we can use as dependency for
features that are broken. This allows to easily disable them
without removing the code.

As no short text is supplied the option will not appear in
menuconfig.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>