powerpc: Create pci_controller_ops.reset_secondary_bus and shim

Add pci_controller_ops.reset_secondary_bus,
shadowing ppc_md.pcibios_reset_secondary_bus.
Add a shim, and changes the callsites to use the shim.

Use pcibios_reset_secondary_bus_shim, as both
pcibios_reset_secondary_bus and pci_reset_secondary_bus
are already taken.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>