Issue #2: Need Operand Dependency Checking Task 1 (#40)

Implementation of Task 1 for full Rename support:

Task 1: Add a arch map -> PRF map to Rename. 

This includes adding a physical register freelist (parameterized to the number). 
When an instruction enters rename, its source arch registers are mapped to the current
physical register for that arch value. Then its destination registers are renamed — 
a new PRF is pulled from the freelist, given to the instruction (via the scoreboard mask) 
and the rename map updated.

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Signed-off-by: Aaron Chan <achn357@gmail.com>
Co-authored-by: Aaron Chan <aaronchan@client-10-229-46-41.tamulink.tamu.edu>
Co-authored-by: Aaron Chan <aaronchan@Aarons-MacBook-Air-2.local>
Co-authored-by: Knute Lingaard <knute.lingaard@sifive.com>
Co-authored-by: Aaron Chan <aaronchan@Aarons-Air-2.attlocal.net>
Co-authored-by: Aaron Chan <aaronchan@client-10-228-106-204.tamulink.tamu.edu>