dist/jlink.sh: Allow overwriting the 'reset' commands

Add a variable to configure the reset commands.
This is required for board that need a hardware reset.

dist/tools/jlink/jlink.sh

@@ -54,6 +54,8 @@
 
 # Set IMAGE_OFFSET to zero by default.
 : ${IMAGE_OFFSET:=0}
+# Allow overwriting the reset commands.
+: ${JLINK_RESET_FILE:=${RIOTTOOLS}/jlink/reset.seg}
 
 # default GDB port
 _GDB_PORT=3333
@@ -167,7 +169,7 @@ do_flash() {
     if [ ! -z "${JLINK_POST_FLASH}" ]; then
         printf "${JLINK_POST_FLASH}\n" >> ${BINDIR}/burn.seg
     fi
-    cat ${RIOTTOOLS}/jlink/reset.seg >> ${BINDIR}/burn.seg
+    cat ${JLINK_RESET_FILE} >> ${BINDIR}/burn.seg
     # flash device
     sh -c "${JLINK} ${JLINK_SERIAL} \
                     -ExitOnError 1 \
@@ -224,7 +226,7 @@ do_reset() {
                     -speed '${JLINK_SPEED}' \
                     -if '${JLINK_IF}' \
                     -jtagconf -1,-1 \
-                    -commandfile '${RIOTTOOLS}/jlink/reset.seg'"
+                    -commandfile '${JLINK_RESET_FILE}'"
 }
 
 do_term() {