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

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

configure.ac is not cross-compile aware, a patch fixing DRI detection
was added in 2009
http://git.buildroot.net/buildroot/commit/package/x11r7/xdriver_xf86-video-mga/xdriver_xf86-video-mga-1.4.9.patch?id=59b0aa7a7ee327688a77dd5d01d0b2032f6535a2

assuming DRI support being present if DRI support was not disabled.

By default configure.ac assumes "auto" which leads to DRI support being
enabled even if DRI support is disabled in buildroot config. This patch
adds --disable-dri to really disable DRI support, fixes:

http://autobuild.buildroot.net/results/5e5/5e5dbc30e1f30f7d2d614f4a9edb7fe439f73d61/
http://autobuild.buildroot.net/results/a8f/a8fab920599e7dc77038f3d2a9a699d6823cf3ef/
http://autobuild.buildroot.net/results/81d/81dbad489412cd28345de364624180cb082b3bb6/
http://autobuild.buildroot.net/results/53f/53fc0031da2b65890223f3183c77eb66cf0b5273/
http://autobuild.buildroot.net/results/544/54481a0f8d690e3878f4616ae1f331705e3c34be/

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