Change OH clock frequency to 40 MHz

Summary of Changes

• Closes #15 (closed)
  • Use a 40MHz clock in the GE21 OH
  • Fix synchronization to the BC0
• Closes #20 (closed)
  • Fix GE21 slow control & improve GE21 sbits deserialization
• Closes #27 (closed)
  • Add a resync counter in the OH
• Closes #30 (closed)
  • Support simultaneous L1A + BC0 in the OH
• Closes #28 (closed)
  • Optional masking of clusters after an L1A

Clock source change

Changes the clock source to

NET "clock_p"   LOC = A10; #dskw clock
NET "clock_n"   LOC = B10; #dskw clock

which corresponds to clockdes1 from the GBTX