Update PRBS, Vcal, mflowgen, JTAG ID

[sgherbst]

This PR makes four distinct updates:

• Pulls in recent updates from the mflowgen branch (custom-geom, custom-init, custom-power steps, using defaults for custom-init and custom-power for now -- @zamyers is working to update those scripts)
• Fixes the issue about the Vcal net (#32) so that it is now an inout net as expected
• Resolves the issue about PRBS updates (#58) so that it is more robust and flexible
• Resolves issues related to setting the JTAG ID to the git commit hash -- #55 (implementation) and #88 (testing the feature update)

[codecov-io]

Codecov Report

Merging #90 into master will decrease coverage by 0.42%. The diff coverage is 45.00%.

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
- Coverage   22.69%   22.26%   -0.43%     
==========================================
  Files          32       33       +1     
  Lines        1873     1909      +36     
==========================================
  Hits          425      425              
- Misses       1448     1484      +36     

Impacted Files	Coverage Δ
dragonphy/jtag.py	0.00% <0.00%> (ø)
dragonphy/git_util.py	61.53% <61.53%> (ø)
dragonphy/views.py	82.92% <90.90%> (+1.51%)	:arrow_up:
dragonphy/subprocess_run.py	22.58% <0.00%> (-58.07%)	:arrow_down:

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[zamyers]

LGTM