mlx4: Subscribe to PXM notifier

mlx4: Subscribe to PXM notifier

With patch titled: "xen/pci: Add PXM node notifier for PXM (NUMA) changes."
there is a notifier which can be used to obtain information
about which NUMA node the device is on.

Usually this kind of information is available prior to the driver
loading, but thanks to the braindead way piix4 emulation works
in QEMU there is no good way of making this work.

Upstream is working on ditching this, but it is a year off or so.

Note that this should not be needed if QEMU q35 platform
is exposed with PCIe bridges in them. The PCIe bridges would contain
the proper PXM information and the hotplugged PCIe device would
snuggly be attached there.

But in the meantime this hack is in place to expose the PXM data.

OraBug: 27200813
Acked-by: Håkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>