Add target for the nRF5340

[northernpaws]

Detailed description

• Adds a target for handling both cores of the nRF5340
• Detects which cores (application & network) are online/offline
• Handles detecting if cores are protected and need to be mass-erased to unlock

I've started adding target support for the nRF5340. Following discussions in #1779, this includes support for detecting if the cores are protected or unprotected, and detecting if the network core is offline and powering it on once the application core is unprotected.

Your checklist for this pull request

• I've read the Code of Conduct
• I've read the guidelines for contributing to this repository
• It builds for hardware native (see Building the firmware)
• It builds as BMDA (see Building the BMDA)
• I've tested it to the best of my ability
• My commit messages provide a useful short description of what the commits do

Closing issues

fixes #1779

TODO

• Implement mass-erasing for unprotecting the cores
• Add the flash and memory layout to the target
• Add target command to bring the network core online if the application core is unprotected

[dragonmux]

Accidentally marked as ready for review and don't see the button to undo that - apologies; we are aware it's not actually ready yet, so just leave a message in the comments when you are ready for it to actually be ready for review.

[northernpaws]

Accidentally marked as ready for review and don't see the button to undo that - apologies; we are aware it's not actually ready yet, so just leave a message in the comments when you are ready for it to actually be ready for review.

No worries, I was able to switch it back to a draft 😄