build-kernel: Prefer local config over ones shipped in kernel sources

This makes the overrides more useful

build/build_kernel_deb.sh

@@ -109,10 +109,10 @@ fi
 
 if [ ! -e .config ]; then
   echo "Configuring kernel"
-  if [ -e "arch/${ARCH}/configs/${DOT_CONFIG}" ]; then
-    cp "arch/${ARCH}/configs/${DOT_CONFIG}" .config
-  else
+  if [ -e "../${DOT_CONFIG}" ]; then
     cp "../${DOT_CONFIG}" .config
+  else
+    cp "arch/${ARCH}/configs/${DOT_CONFIG}" .config
   fi
 fi