KVM: PPC: booke: Mark three local functions "static"

Tag a few functions that are local and don't have a previous prototype
as "static".

No functional change intended.

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202303031630.ntvIuYqo-lkp@intel.com


Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230308232437.500031-1-seanjc@google.com