hosted: assert ntrst as part of connecting

[xobs]

Detailed description

Assert the nTRST when connecting via JTAG. This is required for targets that use this pin to enable the JTAG circuitry.

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• I've read the Code of Conduct
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• It builds for hardware native (see Building the firmware)
• It builds as BMDA (see Building the BMDA)
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[dragonmux]

This LGTM, merging. Thank you for the contribution! This makes quite a nice addition to the CMSIS-DAP backend given it fixes the behaviour of some boards that expose nTRST and have it low and force the debugger to consider the signal a debug enable signal.