[POWERPC] Remove hack to determine the 2nd PHBs bus number

[POWERPC] Remove hack to determine the 2nd PHBs bus number

Now that we have the pci_controller in the exclude function we can easy
figure out if the bus number is the PHB or not.  The old style of using a
variable setup at init time was actually broken and would only work in
specific cases.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>