[PATCH] PCI: use bus numbers sparsely, if necessary

Add a warning if a child bus may be inaccessible because the
parent bridge has wrong secondary or subordinate bus numbers.
Note that this may or may not happen on "transparent" bridges,
as can be seen in bug #5557.

Also, if we do not fix up the assignment of bus numbers, try to
make use of the bus number space available.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>