driver: add support for LTS branches back to 4.4

Still need to pick some configs in travis.yml.

driver.sh

@@ -23,7 +23,13 @@ setup_variables() {
         echo "   LD:"
         echo "       If no LD value is specified, \${CROSS_COMPILE}-ld is used. arm64 only."
         echo "   REPO:"
-        echo "       linux (default) or linux-next, to specify which tree to clone and build."
+        echo "       Nicknames for trees:"
+        echo "         linux (default)"
+        echo "         linux-next"
+        echo "         4.18"
+        echo "         4.14"
+        echo "         4.9"
+        echo "         4.4"
         echo
         echo " Optional parameters:"
         echo "   -c | --clean:"
@@ -79,9 +85,32 @@ setup_variables() {
 
   # torvalds/linux is the default repo if nothing is specified
   case ${REPO:=linux} in
-    "linux") owner=torvalds ;;
-    "linux-next") owner=next ;;
+    "linux")
+      owner=torvalds
+      tree=linux
+      branch=master ;;
+    "linux-next")
+      owner=next
+      tree=linux-next
+      branch=master ;;
+    "4.18")
+      owner=stable
+      tree=linux
+      branch=linux-4.18-y ;;
+    "4.14")
+      owner=stable
+      tree=linux
+      branch=linux-4.14-y ;;
+    "4.9")
+      owner=stable
+      tree=linux
+      branch=linux-4.9-y ;;
+    "4.4")
+      owner=stable
+      tree=linux
+      branch=linux-4.4-y ;;
   esac
+  url=git://git.kernel.org/pub/scm/linux/kernel/git/${owner}/${tree}.git
 }
 
 check_dependencies() {
@@ -112,13 +141,13 @@ mako_reactor() {
 build_linux() {
   CC="$(command -v ccache) $(command -v clang-8)"
 
-  if [[ ! -d ${REPO} ]]; then
-    git clone --depth=1 git://git.kernel.org/pub/scm/linux/kernel/git/${owner}/${REPO}.git
-    cd ${REPO}
+  if [[ ! -d ${tree} ]]; then
+    git clone --depth=1 -b ${branch} --single-branch ${url}
+    cd ${tree}
   else
-    cd ${REPO}
-    git fetch --depth=1 origin master
-    git reset --hard origin/master
+    cd ${tree}
+    git fetch --depth=1 ${url} ${branch}
+    git reset --hard FETCH_HEAD
   fi
 
   git show -s | cat
@@ -138,7 +167,7 @@ build_linux() {
     [[ $ARCH != "x86_64" ]] && cat ../configs/tt.config >> .config
     mako_reactor olddefconfig &>/dev/null
   fi
-  mako_reactor ${image_name}
+  mako_reactor
 
   cd "${OLDPWD}"
 }