ci: update my make job

Signed-off-by: Chris Kay <chris.kay@arm.com>
Change-Id: I52108cac3145c12b6c6e6917010b858efd37122a
diff --git a/cjkay-tf-a-make/Jenkinsfile b/cjkay-tf-a-make/Jenkinsfile
index 72f9ec8..e012cf5 100644
--- a/cjkay-tf-a-make/Jenkinsfile
+++ b/cjkay-tf-a-make/Jenkinsfile
@@ -61,6 +61,24 @@
     }
 
     stages {
+        stage('Prepare Ubuntu') {
+            when {
+                expression {
+                    params.TF_A_SYSTEM.startsWith('ubuntu:')
+                }
+            }
+
+            steps {
+                sh '''
+                    set -eux
+
+                    apt-get update
+                    apt-get install -y --no-install-recommends \
+                        build-essential git
+                '''
+            }
+        }
+
         stage('Checkout') {
             steps {
                 checkout([ $class: 'GitSCM',