* Support DTR in serial passthrough mode to enable programming of Arduino
based devices such as MinimOSD.
Use 'serialpassthrough 5 57600 rxtx 56' and then use Ardino to program MinimOSD
Use 'serialpassthrough 5 115200' and then use MWOSD configurator to setup
* Fix comment for CDC_SetCtrlLineStateCb routine
* Handle F7 CDC interface
* Use strToPin() to allow easy port/pin specification
* Fix use of CDC_SetCtrlLineStateCb for all processor types
* Only set baud when specified
* Fix unit tests for cli
* Only register callback if needed
* Fix white space
* Provide implementation of IOConfigGPIO in SITL
* Update serialpassthrough help text
* DTR handling through serial drivers
* Fix F3, F7 and SITL builds
* If serialpassthrough command specifies baud rate of 0, set baud rate over USB. MWOSD configurator can now access config and reflash MinimOSD without rebooting and changing baud rate.
* Fix F3 build
* Fix failing unit tests
* Use resources to declare DTR pin assignment
* Don't assert DTR during normal operation as MW_OSD doesn't like it
* MW_OSD must be built with MAX_SOFTRESET defined in order to support DTR resets
* Minimise changes after dropping DTR pin param from serialpassthrough cmd
* Remove DTR pin param from serialpassthrough cmd
* Treat ioDtrTag as boolean in conditional statements
* Tidy buffer check
* Check buffer size in CDC_Itf_Control
* Fix unit test
* Add documentation for DTR
* Add note on MAX_SOFTRESET to documentation
* Remove superfluous function definitions
* Fix tabs
* Fix tabs
* Removed superfluous entried from vtable
* Backout whitespace changes unrelated to this PR
* Pass true/false to IOWrite()
* Fix line coding packing
* Add LINE_CODING structure defintion
* Revise serial documentation
* Prevent tx buffer overflow in serialPassthrough()
* Revert change unrelated to PR
* Review feedback from ledvinap
* Fix unit test
* Use PINIO to drive DTR
* Fix unit test
* Remove change unrelated to PR
* Fix SITL build
* Use shifted bits for mask definition
* Fix serialpassthrough documentation
* Only compile PINIO functionality if USE_PINIO defined
* IOConfigGPIO not needed
* Move cbCtrlLine callback to cli.c
* serialPassthrough params changed
* Check packed structure size
* Fix unit test
* Tidy up baud rate handling
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