xdriver_xf86-video-geode: only build on i386

This package builds with -m32. In buildroot, we don't have multilib
support so only the 64-bit libraries are available, which can't be
linked against these 32-bit object files.

I've tested this with the Sourcery and buildroot toolchains - neither
works.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>