RTT Viewer is available, but pyocd rtt is not

[HaoYDai]

pyocd> read8 0x20000040 64
20000040:  40 00 00 20  40 00 00 20  30 00 00 00  0a 00 00 00    |@.. @.. 0.......|
20000050:  ac 25 00 20  78 13 00 20  2c 00 00 00  53 45 47 47    |.%. x.. ,...SEGG|
20000060:  45 52 20 52  54 54 00 00  00 00 00 00  02 00 00 00    |ER RTT..........|
20000070:  02 00 00 00  a4 39 01 08  10 08 00 20  00 04 00 00    |.....9..... ....|

Fundamental problem: first character of the cb_id was not in the memory of this read
I saw that someone else had fixed it, but I felt that the fix was not perfect, and the change was large, but it was actually a minor bug

[HaoYDai]

#1729