Performance-monitoring counters

[CircuitCoder]

Implement following [h]pmcounterX:

instret: Retired instruction
pmcounter3: IF cache misses
pmcounter4: Cached load
pmcounter5: Cached store
pmcounter6: Cached load misses
pmcounter7: Cached store misses
pmcounter8: Uncached load
pmcounter9: Uncached store
pmcounter10: In-flight instruction saturated cycles
pmcounter11: Issue stall cycles (Stalled by a full reservation station, or the in-flight limit is reached)
pmcounter12: Issue FIFO empty cycles
pmcounter13: ROB empty cycles
pmcounter14: Retired branch count
pmcounter15: Retired branch misperdicts
pmcounter16: Issued BHT misses
pmcounter17: Issued RAS misses
pmcounter18: Exceptions
pmcounter19: X_CALL exceptions
pmcounter20: Interrupts