Ingo's CPU scheduler update (in -mm kernels) needs a new sched_clock()
function which returns nanoseconds.

The patch provides implementations for ppc, ppc64, x86_64 and sparc64.

The x86_64 version could have overflow issues, the calculation is done in
32bits only with an multiply.  But I hope it's good enough for the scheduler

The ppc64 version needs scaling: it's only accurate for 1GHz CPUs.