runtime-perf: add linux perf events

This introduces support for the linux perf API. This enables and
exposes the follow block level performance counters through ctrlport
    * L1 Data-Cache Miss Rate
    * Branch Mispredict Rate
    * CPU cycles (not subject to freq scaling)
    * SW Context Switches
    * SW CPU Migrations

Note that in cmake we need to explicitly check for required headers because
they may not always be there (ex: ubuntu 12.04 doesn't package
a generic hw_breakpoint.h)

There's also a new throughput (wall clock time) counter
docs: s/is/it/ typo
runtime: ifdef fence a linux only vector for new perf events
runtime: expose new counters through swig