NuttX: Allow different board prototype names from main build config

src/firmware/nuttx/CMakeLists.txt

@@ -66,10 +66,14 @@ add_custom_command(OUTPUT ${BOARD}.bin
 	DEPENDS ${FW_NAME}
 	)
 
+if (NOT FW_PROTOTYPE)
+	set(FW_PROTOTYPE ${BOARD})
+endif()
+
 if (TARGET parameters_xml AND TARGET airframes_xml)
 	add_custom_command(OUTPUT ${fw_file}
 		COMMAND ${PYTHON_EXECUTABLE} ${PX4_SOURCE_DIR}/Tools/px_mkfw.py
-			--prototype ${PX4_SOURCE_DIR}/Images/${BOARD}.prototype
+			--prototype ${PX4_SOURCE_DIR}/Images/${FW_PROTOTYPE}.prototype
 			--git_identity ${PX4_SOURCE_DIR}
 			--parameter_xml ${PX4_BINARY_DIR}/parameters.xml
 			--airframe_xml ${PX4_BINARY_DIR}/airframes.xml