scripts: Add a bash function to sync external code

Added a bash function in integration test script to checkout source code
of a GIT repo with specified branch and commit.

Signed-off-by: Michael Zhao <michael.zhao@arm.com>

scripts/run_integration_tests_aarch64.sh

@@ -12,6 +12,46 @@ EDK2_BUILD_DIR="$WORKLOADS_DIR/edk2_build"
 
 mkdir -p "$WORKLOADS_DIR"
 
+# Checkout source code of a GIT repo with specified branch and commit
+# Args:
+#   $1: Target directory
+#   $2: GIT URL of the repo
+#   $3: Required branch
+#   $4: Required commit (optional)
+checkout_repo() {
+    SRC_DIR="$1"
+    GIT_URL="$2"
+    GIT_BRANCH="$3"
+    GIT_COMMIT="$4"
+
+    # Check whether the local HEAD commit same as the requested commit or not.
+    # If commit is not specified, compare local HEAD and remote HEAD.
+    # Remove the folder if there is difference.
+    if [ -d "$SRC_DIR" ]; then
+        pushd $SRC_DIR
+        git fetch
+        SRC_LOCAL_COMMIT=$(git rev-parse HEAD)
+        if [ -z "$GIT_COMMIT" ]; then
+            GIT_COMMIT=$(git rev-parse remotes/origin/"$GIT_BRANCH")
+        fi
+        popd
+        if [ "$SRC_LOCAL_COMMIT" != "$GIT_COMMIT" ]; then
+            rm -rf "$SRC_DIR"
+        fi
+    fi
+
+    # Checkout the specified branch and commit (if required)
+    if [ ! -d "$SRC_DIR" ]; then
+        git clone --depth 1 "$GIT_URL" -b "$GIT_BRANCH" "$SRC_DIR"
+        if [ "$GIT_COMMIT" ]; then
+            pushd "$SRC_DIR"
+            git fetch --depth 1 origin "$GIT_COMMIT"
+            git reset --hard FETCH_HEAD
+            popd
+        fi
+    fi
+}
+
 build_edk2() {
     EDK2_REPO="https://github.com/tianocore/edk2.git"
     EDK2_DIR="edk2"