SWD Fixes

[adamgreen]

I code reviewed ARM's DAPLink sources tonight and noticed a few differences between it and my implementation. This commit attempts to bring it inline with their implementation:

• Increase idle at end of line reset to 8 clocks instead of 2. The spec indicates that it needs to be 2 or more but this was the second example of 8 being used instead that I have encountered.
• Increase the number of clock cycles with SWDIO held high from 50 to 51 during line reset. Again the spec indicates 50 or more but DAPLink uses 51 so that might have been done based on real world problems they encountered.

[adamgreen]

Thanks for testing and merging.