pci: Add a probing code that seeks for an specific bus

This patch adds a probing code that seeks for an specific pci bus. It
still needs testing, but it is hoped that this will help to identify the
memory controller with Xeon 55xx series.

Signed-off-by: Aristeu Sergio <arozansk@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>