Upload: PyOCD: Honor OUTPUT_EXT

[ccli8]

Summary of changes

This PR tries to honor OUTPUT_EXT defined in targets.json5 for PYOCD upload method flash. If it is defined, use image file with the specified extension .<OUTPUT_EXT> for flash, or default to .bin.

Pull request type

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

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[multiplemonomials]

Hmm... I assume that this MR is being submitted because there's a target using .hex only as the output extension, and that's breaking the upload methods that use the BIN_FILE argument. And the fact is, this is very easy to do when writing an upload method, because gen_upload_target() accepts the bin file in the parameters list.

What if we instead change the signature of gen_upload_target to something like

function(gen_upload_target TARGET_NAME BINARY_FILE)

where BINARY_FILE was the path to the bin or the hex file, whichever exists?

this function would be changed to something like

# Generate an upload target for an executable
function(mbed_generate_upload_target target)
    if ("${MBED_OUTPUT_EXT}" STREQUAL "" OR MBED_OUTPUT_EXT STREQUAL "bin")
        gen_upload_target(${target} ${CMAKE_CURRENT_BINARY_DIR}/$<TARGET_FILE_BASE_NAME:${target}>.bin)
    else()
        gen_upload_target(${target} ${CMAKE_CURRENT_BINARY_DIR}/$<TARGET_FILE_BASE_NAME:${target}>.hex)
    endif()
endfunction()

Then we would refactor all the upload methods to be able to handle a bin or hex file, and the logic in them could be a lot simpler.

[ccli8]

Create #331 to apply above suggestion

[multiplemonomials]

Closing this now since #331 is merged