build: support out of tree builds

Change-Id: Ibf07f1056567eb25106b8039c14e54411243d831
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/generate_makefile.sh b/generate_makefile.sh
index e0f0511..4816919 100755
--- a/generate_makefile.sh
+++ b/generate_makefile.sh
@@ -1,5 +1,7 @@
 #!/bin/sh
 
+cd $1
+
 toplevel_dirs=xyz
 interfaces=`find $toplevel_dirs -name "*.interface.yaml"`