Add support for DFU upload methods

[multiplemonomials]

Summary of changes

This PR adds support for uploading over DFU. This is a prerequisite for working with Arduino STM32H7 boards, such as Portenta and Giga. These boards support DFU both via the Arduino bootloader and via the STMicro ROM bootloader. There currently isn't a defined way to enter the Arduino bootloader from Mbed however, so we'll have to rely on the ROM bootloader for now.

dfu-utils seems to be the standard way of doing this, so I added support for it in CMake. However, STM32Cube also supports DFU uploading, so it wasn't too tough to add an upload method for it as well.

Impact of changes

• New upload method DFU_UTIL
• New upload method STM32CUBE_DFU

Migration actions required

Documentation

Updated the upload methods page: https://github.com/mbed-ce/mbed-os/wiki/Upload-Methods

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[X] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

Successfully uploaded code using these upload methods to my Arduino Giga.