DP: error handling tidying.
DP: error handling tidying.

- Writing fields that need to be set when clearing sticky err in JTAG.
- Comment about unpredictable state of APs after an abort.

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