Add the ability to create SimPoint basic block vector (BBV) files from gem5.

This patch adds SimPoint profiling functionality to the atomic CPU model.  Normally one has to use another tool like valgrind or pinpoints to perform this analysis.  Using the --simpoint_profile and --simpoint_interval options, after running simulation a simpoint.bb.gz file will be created in the gem5 output directory.  This file can then be fed to the simpoint tool to identify program sections representative of overall program behavior.

Ran a few benchmarks, output simpoint file and selected simpoints seem ok.