sb/amd/sr5650: Allow resource allocator to assign bus numbers

sb/amd/sr5650: Allow resource allocator to assign bus numbers

At some point in the past disconnected PCIe bridges were completely
disabled to work around a hang on bridge probe.  This hang was
resolved at some point, and the disconnected PCIe bridges should
be enabled to receive a bus number per the RPR.

This resolves a slew of warnings in the Linux boot log regarding
invalid bridge configurations for disconnected bridge devices.

Change-Id: Ic26e2d62ec5ddb9f22275c2afec7d560326263c7
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: https://review.coreboot.org/12673
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>