powerpc/powermac: Make some functions static

These functions can all be static, make it so. Fix warnings treated as
errors with W=1:

  arch/powerpc/platforms/powermac/pci.c:1022:6: error: no previous prototype for ‘pmac_pci_fixup_ohci’
  arch/powerpc/platforms/powermac/pci.c:1057:6: error: no previous prototype for ‘pmac_pci_fixup_cardbus’
  arch/powerpc/platforms/powermac/pci.c:1094:6: error: no previous prototype for ‘pmac_pci_fixup_pciata’

Remove has_address declaration and assignment since it's not used.
Also add gcc attribute unused to fix a warning treated as error with
W=1:

  arch/powerpc/platforms/powermac/pci.c:784:19: error: variable ‘has_address’ set but not used
  arch/powerpc/platforms/powermac/pci.c:907:22: error: variable ‘ht’ set but not used

Suggested-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>