Added additional performance counters. Ch 5 is update todate with these changes.

Created by: rosethompson

• Cleaned up branch predictor performance counters.
• Added support for branch target buffer stats.
• Fixed bug in performance counter script.
• Reordered performance counters and added space for new ones.
• Added store stall to performance counters.
• Added csr write counter, sfence vma counter, interrupt counter, and exception counter.
• Added fence counter.
• Added the i and d cache cycle counters.
• Added divide cycle counter.
• Renamed BTB misprediction to BTA.