package/x11r7/xdriver_xf86-video-savage: disable DRI support when not available

Fixes
http://autobuild.buildroot.net/results/ecd/ecdb6977d282c276cbdf1f3dd0ccfaddff1d1ac5/



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>