CLI Branch Predictor bugfixes and options' description enhancements

[thanoskyprianos]

• There was a segfault happening when dumping branch predictor stats and the branch predictor was disabled
• The initial state check of the smith 2 branch predictor was wrong
• I improved the descriptions of the d-cache and l2-cache options that did not mention the writeback feature was configurable, even though the implementation is there.

[ppisa]

Thanks for the contribution, generally looks good for me but I suggest to combine two mentioned patches together.