[POWERPC] pci32: Remove obsolete PowerMac bus number hack

The 32 bits PCI code carries an old hack that was only useful for G5
machines.  Nowdays, the 32 bits kernel doesn't support any of those
machines anymore so the hack is basically never used, so remove it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>