Revert "Revert "FVP Linux and TFTF YAML Support""

This reverts commit a2946b2b5d0b3b9daa7ede0780ee4c535f637122.

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: I44c9b346b5548cc961f88eb40ce723943e66f2d0
diff --git a/utils.sh b/utils.sh
index c0fd619..47a2df9 100644
--- a/utils.sh
+++ b/utils.sh
@@ -337,6 +337,8 @@
 "--hfa"
 )
 
+docker_registry="${docker_registry:-}"
+
 # Define toolchain version and toolchain binary paths
 toolchain_version="9.2-2019.12"