Upload: Mbed: Honor OUTPUT_EXT for flash (mbed-ce#328)

In Mbed flash, if OUTPUT_EXT is defined in targets.json5, use image file with this extension <target>.<OUTPUT_EXT> for flash, or default to <target>.bin.

Author: ccli8

tools/cmake/upload_methods/UploadMethodMBED.cmake

@@ -20,7 +20,7 @@ function(gen_upload_target TARGET_NAME BIN_FILE)
 
 add_custom_target(flash-${TARGET_NAME}
 COMMAND ${Python3_EXECUTABLE} -m install_bin_file
-${BIN_FILE}
+$<IF:$<BOOL:${MBED_OUTPUT_EXT}>,${CMAKE_CURRENT_BINARY_DIR}/$<TARGET_FILE_BASE_NAME:${TARGET_NAME}>.${MBED_OUTPUT_EXT},BIN_FILE>
 ${MBED_TARGET}
 ${MBED_RESET_BAUDRATE}
 ${MBED_TARGET_UID}