hardware_gen.py: fail execute_process on error

Fail with an error if the script returns an error. Additionally hook
stdio up to execute process to allow easier use of python debugging
tools if required.

src/arch/arm/config.cmake

@@ -130,7 +130,14 @@ if (DEFINED KernelDTSList)
     # Generate devices_gen header based on DTB
     execute_process(
         COMMAND ${PYTHON} "${HARDWARE_GEN_PATH}" --dtb "${KernelDTBPath}" --compatibility-strings "${compatibility_outfile}" --output "${device_dest}" --config "${config_file}" --schema "${config_schema}"
+        INPUT_FILE /dev/stdin
+        OUTPUT_FILE /dev/stdout
+        ERROR_FILE /dev/stderr
+        RESULT_VARIABLE error
     )
+    if (error)
+        message(FATAL_ERROR "Failed to generate: ${device_dest}")
+    endif()
     file(READ "${compatibility_outfile}" compatibility_strings)
 
     include(src/drivers/config.cmake)