pciutils: disallow on Blackfin

Even though some Blackfin processors have PCI interfaces, the PCI
support is not supported by the Linux kernel: it has been marked as
broken since 2008. This means there's probably little interest for PCI
on Blackfin, and consequently little interest about getting pciutils
to build.

Fixes http://autobuild.buildroot.net/results/a27/a27ce61967ef8f780887f7681c8b0edd91656be6/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>