Add board enable for ASUS A7V8X-MX.

Use the same trick as for the MX-SE variant.
Despite being mentioned as supported on
http://flashrom.org/Supported_hardware flashrom fails to detect the
flash chip without this.

Signed-off-by: François Revol <revol@free.fr>
Acked-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>

git-svn-id: svn://flashrom.org/flashrom/trunk@1766 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1