COM bus instability

[bunnie]

COM bus instability was noted on an instance of the EC-SOC link with a particular routing seed.

• Make the outside-facing registers of the COM block ODDR2/IDDR2 so that all fabric routing delays are eliminated.
• Review the EC for opportunities to tighten up the timing loop, and see if nextpnr/yosys has introduced options yet for I/O timing constraints since the block was written.
• consider reducing the clock rate of the COM bus.

[bunnie]

this was fixed long ago, but forgotten to close