targets/dri-r600: Convert to automake

v2: Andreas Boll <andreas.boll.dev@gmail.com>
    - Provide compatibility with scripts for the old Mesa build system
diff --git a/configure.ac b/configure.ac
index 9c9791b..bb287d7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2057,6 +2057,7 @@
 		src/gallium/targets/dri-i915/Makefile
 		src/gallium/targets/dri-nouveau/Makefile
 		src/gallium/targets/dri-r300/Makefile
+		src/gallium/targets/dri-r600/Makefile
 		src/gallium/targets/opencl/Makefile
 		src/gallium/winsys/Makefile
 		src/gallium/winsys/i915/drm/Makefile