Add script to fetch PackChk/SVDConv from their release location.

diff --git a/Jenkinsfile b/Jenkinsfile
index 375bf37..be71d42 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -313,6 +313,7 @@
             }
             steps {
                 checkoutScmWithRetry(3)
+                sh('./CMSIS/Utilities/fetch_devtools.sh')
                 sh('./CMSIS/RTOS/RTX/LIB/fetch_libs.sh')
                 sh('./CMSIS/RTOS2/RTX/Library/fetch_libs.sh')