functions: Run prereqs as an init step

This prevents prereqs from running in parallel when we build the target.

Change-Id: I950ca4d233b7d581e18061b7521190ee29b5e529
diff --git a/vars/functions.groovy b/vars/functions.groovy
index 26e7f71..8724934 100644
--- a/vars/functions.groovy
+++ b/vars/functions.groovy
@@ -78,7 +78,7 @@
 
 def buildTarget(targetName) {
     def nprocs = sh(returnStdout: true, script: 'nproc').trim()
-    sh "bash -c 'source build/setup.sh; m -j${nprocs} prereqs ${targetName}; exit \$?'"
+    sh "bash -c 'source build/setup.sh; m -j${nprocs} ${targetName}; exit \$?'"
 }
 
 def manifestUrlFromBoardName(boardName) {
@@ -157,6 +157,7 @@
                 container('debian') {
                     stage('Init') {
                         initSourceTree(boardName, needsNative)
+                        sh "bash -c 'source build/setup.sh; m prereqs; exit \$?'"
                     }
 
                     stage('Build') {