PCI: Add a generic weak pcibios_fixup_bus()

Multiple architectures define this as an empty function, and I'm adding
another one as part of the RISC-V port.  Add a __weak version of
pcibios_fixup_bus() and delete the now-obselete ones in a handful of
ports.

The only functional change should be that microblaze used to export
pcibios_fixup_bus().  None of the other architectures exports this, so I
just dropped it.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

arch/tile/kernel/pci_gx.c

@@ -1038,11 +1038,6 @@ alloc_mem_map_failed:
 }
 subsys_initcall(pcibios_init);
 
-/* No bus fixups needed. */
-void pcibios_fixup_bus(struct pci_bus *bus)
-{
-}
-
 /* Process any "pci=" kernel boot arguments. */
 char *__init pcibios_setup(char *str)
 {