pci: check the bus number for pcie mechanism

* fallback to mechanism 1 for out of range bus numbers
* Support for the fallback is mandatory according to the PCIe specification.
* Should help with #9929 and #9930
Revert "BMenu return only enabled items"

Patch by "stimut"

This reverts commit abc26ba8ad02a8394a30dece78ba443fc099b81d.

Reverting this patch fixes #6610
BMenu: Don't hit test separator items

Fixes #4147 while not causing the regression described in #6610
like hrev35248 did.