powerpc/powernv: Make pnv_pci_sriov_enable() and friends static

The kernel test robot noticed these are non-static which causes Clang to
print some warnings. These are called via ppc_md function pointers so
there's no need for them to be non-static.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200705133557.443607-1-oohall@gmail.com