Move TPIU configuring to set_swo_clock() method.
Move TPIU configuring to set_swo_clock() method.

- TPIU should not have been configuring for SWO in the init() method.
- Improved some doc comments.

mbedmicro/pyOCD,mbedmicro/pyOCD,mesheven/pyOCD,pyocd/pyOCD,flit/pyOCD,mesheven/pyOCD,pyocd/pyOCD,mesheven/pyOCD,flit/pyOCD,mbedmicro/pyOCD