Add utility functions to qemu-timer.c for nanosecond timing.
Add qemu_clock_deadline_ns to calculate deadlines to
nanosecond accuracy.
Add utility function qemu_soonest_timeout to calculate soonest deadline.
Add qemu_timeout_ns_to_ms to convert a timeout in nanoseconds back to
milliseconds for when ppoll is not used.
Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>