powerpc/pseries: Make IOV setup routines static

These are only used locally. It fixes these W=1 compile errors :

../arch/powerpc/platforms/pseries/setup.c:610:17: error: no previous prototype for ‘pseries_get_iov_fw_value’ [-Werror=missing-prototypes]
  610 | resource_size_t pseries_get_iov_fw_value(struct pci_dev *dev, int resno,
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~
../arch/powerpc/platforms/pseries/setup.c:646:6: error: no previous prototype for ‘of_pci_set_vf_bar_size’ [-Werror=missing-prototypes]
  646 | void of_pci_set_vf_bar_size(struct pci_dev *dev, const int *indexes)
      |      ^~~~~~~~~~~~~~~~~~~~~~
../arch/powerpc/platforms/pseries/setup.c:668:6: error: no previous prototype for ‘of_pci_parse_iov_addrs’ [-Werror=missing-prototypes]
  668 | void of_pci_parse_iov_addrs(struct pci_dev *dev, const int *indexes)
      |      ^~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210104143206.695198-22-clg@kaod.org