timecounting: add getbinruntime(), getnsecruntime()

timecounting: add getbinruntime(), getnsecruntime()

The networking people want a fast, monotonic clock that only advances
while the system is not suspended.  The runtime clock satisfies most
of these requirements, so introduce getnsecruntime() to provide a fast
means for reading it.

Based on patches from jca@ and claudio@.

ok yasuoka@