[LinuxBIOS] Adding a config option

[Richard Smith]

I'ts been awhile since I've messed with the config system and having
some difficulity adding a new config option.

I have modified the epia-m auto.c to have a ifdef wrapper around the
section that disables the firewire bridge.   I called it
DISABLE_FIREWIRE.  I added uses DISABLE_FIREWIRE to the Options.lb and
setup a defaut.

I then created a new target called epia-ml that just uses the epia-m
mainboard but would disable the firewire disable section.

But when I run buildtarget I still get:

build_dir=via/epia-ml/epia-ml
Configuring TARGET epia-ml
Will place Makefile, crt0.S, etc. in via/epia-ml/epia-ml
===> ERROR: Can't use undefined option DISABLE_FIREWIRE
via/epia-ml/Config.lb:0
src/mainboard/via/epia-m/Options.lb:0

Where else do I  have to add my new config option so the buld system
knwos about it?