dist/tools: Add stm32loader flash utility

dist/tools/flake8/check.sh

@@ -23,7 +23,7 @@ cd $RIOTBASE
 : "${RIOTTOOLS:=${RIOTBASE}/dist/tools}"
 . "${RIOTTOOLS}"/ci/changed_files.sh
 
-EXCLUDE='^(.+/vendor/|dist/tools/cc2538-bsl|dist/tools/mcuboot|dist/tools/uhcpd)'
+EXCLUDE='^(.+/vendor/|dist/tools/cc2538-bsl|dist/tools/mcuboot|dist/tools/uhcpd|dist/tools/stm32loader)'
 FILEREGEX='(\.py$|pyterm$)'
 FILES=$(FILEREGEX=${FILEREGEX} EXCLUDE=${EXCLUDE} changed_files)