Updating RAMCloud::Cycles to use rdtscp.
Updating RAMCloud::Cycles to use rdtscp.

rdtscp takes 12 ns instead of 7 ns for rdtsc on the rc cluster, but it ensures
that all previous instructions have executed before it runs.

utah-scs/RAMCloud,utah-scs/RAMCloud,utah-scs/RAMCloud,utah-scs/RAMCloud,utah-scs/RAMCloud,utah-scs/RAMCloud