Currently if we claim a slot for a PCI driver, we never let it go properly,
this prevents the fallback probe from reusing the slot, even though it
isn't claimed for that pci slot.

So if you set the modesetting driver to point at a specific kms device,
that isn't a PCI device (i.e. USB dongle), then the modesetting driver
loads, the pci probe tries to bind the config slot to the primary PCI
device, however we then check the kms device bus id to discover it
isn't valid. However we don't remove the claim on the slot. Next the
old probe function is called and there is no slots to claim.

This patch fixes that and converts the pciSlotClaimed boolean into
a counter, and changes the unclaim api to take a device pointer
to remove from the entity.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>