Test FFE and phase doubling

[standanley]

This pull request does 3 things:

• Add FFE_SIMPLE test to test FFE behavior
• Modify MM_CDR test to update FFE weights through JTAG
• Add PHASE_DOUBLING test to confirm that phase doubling increases ENOB

[codecov-commenter]

Codecov Report

Merging #101 into master will increase coverage by 0.88%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #101      +/-   ##
==========================================
+ Coverage   22.22%   23.10%   +0.88%     
==========================================
  Files          33       34       +1     
  Lines        1908     1930      +22     
==========================================
+ Hits          424      446      +22     
  Misses       1484     1484              

Impacted Files	Coverage Δ
dragonphy/remap.py	100.00% <100.00%> (ø)

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[sgherbst]

@standanley Thanks for these updates for the delay in reviewing. Added a couple of comments in the code.