Plru changes

Created by: khandelwaltanuj

Hello,

this pull request contains following updates: There is are couple changes

1. In the case of a read miss, plru is updated when the refill response is received wihtout an error
2. In the case of CMO_PREFETCH hit, plru is updated (correction after an RTL bug fix)

And first model of a dirty bit prediction (it is still incomplete, as document is not complete)

Thanks and Regards Tanuj Khandelwal