[MIPS] IP32: Enable PCI bridges

Fixe MACE PCI addressing by adding the bus number parameter.
Remove check of the used slot since every slot should be valid.
Converted mkaddr from #define to inline function.

Signed-off-by: Giuseppe Sacco <eppesuig@debian.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>