powerpc/lib: Fix randconfig build failure in sstep.c

Under some configs we need to explicitly include cpu_has_feature.h,
otherwise we fail with:

  arch/powerpc/lib/sstep.c:1992:7: error: implicit declaration of function 'cpu_has_feature'

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
1 file changed